How Private Are Sites' Membership Lists?

Slashdot contributor Bennett Haselton has written an essay on a subtle privacy issue affecting many websites (including Slashdot!) He says "Suppose your girlfriend called up Match.com and said, "I think my boyfriend might be cheating on me. His e-mail address is joeblow - at - aol - dot - com. Can you tell me if he's a member?" And Match.com phone support told her, "Why, yes, he is a member. You'd better have a talk with him." After you had gotten over the guilt of getting caught -- I mean, the guilt of cheating -- would you not feel like Match.com had violated your privacy by telling a third party that you were a member?" Keep reading to see what he's getting at and to decide if and when it's a problem.

Something like this is actually possible with quite a few well-known sites -- given a person's e-mail address, it is possible to find out if they have an account with Match.com, PayPal, Netflix, eBay, Amazon, and Google (and, by the way, Slashdot [CT: We'd fix it if I thought it mattered]). For some of those sites, it may even be possible to take a long list of e-mail addresses and use an automated process to find out which of those addresses have accounts with those sites (something I didn't want to risk trying myself, but as a general rule, if you can do it once, you can do it many times, at least if you do it slowly enough). It does not enable the attacker to extract addresses from a site's membership rolls, which is a much more serious type of breach -- in this case, the attacker would have to already know a list of e-mail addresses, and would only be able to find out which of those addresses have accounts with a given service. And it definitely wouldn't enable an attacker to extract more sensitive information like passwords or personal data. But the ability to get a yes/no answer for whether an e-mail address belongs to a member of a given site, should be something that the site designer should take into account. I'm not even saying that it should necessarily be considered a security hole in most cases, just that it should be something that the site designers decide whether or not they want to permit it -- not something that was left in the open accidentally. Representatives from PayPal and Netflix assured me that they knew about the possibility of this attack and had countermeasures to detect it. In the case of Match.com, on the other hand, I would argue it looks like an oversight. For other sites, whether it's a security hole or not depends on your point of view.

There are three main causes for concern with this issue. The first is simple privacy -- for a site like Match.com, a person may not want other people to be able to find out that they're a member. The second is the possibility of making phishing attacks easier. If a phisher sends spam to a huge number of recipients, hoping to trick them into entering their login details on a counterfeit site, then generally their success rate would be proportional to the number of recipients who are members of that site (of which a certain percentage will be duped into entering their login info), but the speed at which the phishing site is shut down would be proportional to the total number of recipients (since any recipient would carry the same likelihood of reporting the phishing site to an ISP and helping to get it shut down). So if the phisher could find out which addresses on their list belong to actual members of a given site, and send mail to just those people, they could get more successful attacks in proportion to the number of e-mails sent. This is especially true of "puddle phishing" attacks, where only a small percentage of recipients are likely to be members of the site being phished. The third possibility is that the data could be valuable to spammers wanting to advertise a competing site -- a spammer advertising a dating site, for example, could get more band for their buck by advertising only to Match.com members. (Maybe even try a hybrid spam-with-just-a-hint-of-phish -- spam that says "Rejected a lot on Match.com?" to make the user think at first that the e-mail really is from Match.com, but then steer them towards a competitor.)

With a build-up like this, the attack is disappointingly simple. (In fact, I listed the possible consequences of the attack first, because otherwise the attack itself is too easy to dismiss.) If you haven't already guessed at least one of these methods, the three easy ways to find out if an e-mail address is associated with an account at a given site, are:

• Try to create a new account with that e-mail address. See if you get an error message saying the address is already associated with an account.
• Log in under an existing account, and try to switch to another e-mail address. See if you get an error message saying the address is already associated with an account.
• Use the forgot-your-password feature to request a password be sent to a given e-mail address. See if you get an error message saying that address is not associated with an account.

Each attack works better if you can avoid triggering an e-mail message sent to the e-mail address in question, whether in a success or failure condition. For example, if the forgot-your-password form only accepts an e-mail address as input, then if the e-mail address you enter really does belong to a member, a password reset e-mail will be sent to that member. That won't prevent you from continuing your attack, but if enough Match.com members get password reset e-mails that they didn't request, some of them will let Match.com know what is going on, and Match.com might find a way to stop the attack in progress. On the other hand, suppose the password-reset form requires an e-mail address and a birthdate, and if you enter an e-mail address without a birthdate, you get one error message telling you that the birthdate was missing, and another error message if the e-mail address you entered is not associated with an account. This avoids triggering an e-mail message to the user in either case, and increases the chance that you can carry on the attack longer without being noticed. And once you've confirmed that someone is a member, this type of password reset form would also let you use trial and error to determine their birthdate as well, something that might make identity theft easier later on. (This, by the way, is exactly how the current Match.com password reset form works. Match.com did not respond to requests for comment.)

With most popular sites that I tested, at least one of the above methods fail, but at least one other method succeeds. On Netflix, for example, the forgot-your-password form requires you to enter a last name and a credit card number, so that form can't be used to find out who is a member. On the new member signup page, though, you can enter an e-mail address and be told whether that e-mail address already belongs to a member. With Match.com, on the other hand, I already mentioned the weakness in the password-reset form, but if I tried to sign up for a new account but I didn't correctly pass the Turing test (reading numbers off a graphic and entering them in a text field), Match.com wouldn't tell me if the e-mail address was associated with an existing account. So that form could not be used to sift through 100,000 addresses and find which ones were Match.com members, but it could be used to find out if an individual person was a subscriber.

There are at least two simple countermeasures to this type of attack. The first is to require a Turing test when a user creates a new account, requests a password reset, or changes their e-mail address on file, and make sure that if the Turing test isn't completed correctly, then no error message is displayed about whether a given e-mail address does or does not exist in the system. This makes it hard for attackers to sift through a mountain of e-mail addresses finding out which ones already belong to accounts, but it still enables someone to check if someone is a member, one person at a time. For sites where that would be a privacy concern (again I'm thinking of Match.com), the other solution is better: send an error message to the e-mail address entered, not displayed to the user in their browser. If you try to sign up as [e-mail], and that address is already associated with an account, then display the normal message telling the user to check their inbox for confirmation -- but then send them a message saying their address is already in the system. eBay, for example, gets this right on their "forgot your userid" page -- if you enter an e-mail address not associated with an eBay account, it simply says, "eBay just sent your User ID to [e-mail]. Check your email to get your User ID." (On the other hand, eBay's new user signup page lets you check if an e-mail address is assigned to an existing member, without needing to pass a Turing test.)

Netflix, eBay and PayPal also responded to say that they had monitors in place to detect "suspicious" activity, saying that even in cases where the forms did not require a Turing test, they could dynamically detect if someone were using a script to submit the form over and over to harvest data, but they declined to go into more detail. It seems to me this could work for forms that require you to be logged-in, but not for forms that don't. For example, on the Netflix new user page, how would they detect if it's the same person submitting e-mail addresses over and over again? Not by IP address -- you can use Tor and farms of open proxies scattered across the Internet to make it appear as if you're coming from lots of different IP addresses. However, consider the PayPal add-a-new-email-address form. This form does not require a Turing test, and does give you an error message if you try to add an address associated with another account. At first I thought this might be a loophole that an attacker could use to find all the PayPal users in a long list of addresses, but PayPal told me that if you do this enough times under the same account, eventually you will hit a limit where the form starts requiring a Turing test. I never got high enough to hit that limit. However, in this case the "dynamic detection" could actually work -- because you can only perform this action while logged in, and after you hit the limit, to continue testing more addresses would require another PayPal account -- and creating additional throwaway PayPal accounts does require a Turing test for each one. So I'll take their word for it that that attack is blocked, although, it seems to me it would be easier just to require a Turing test on the add-a-new-address page.

On the other hand, perhaps in the case of a site like Netflix, it's not something that users really need to worry about, if the company has no problem with it. Big deal, an attacker can find out whether you're a Netflix user -- but that's not a huge privacy violation, it's not like I shamefully hide those red envelopes under my shirt while I'm scurrying back from the mailbox. Now, a spammer can take a list of addresses and run them through the form to find out who is a Netflix customer, and then spam those users trying to lure them to a competing service -- but that's Netflix's problem, not ours, isn't it? (Well, it's our problem that we get the spam. But without using this attack, the alternative was that the spammer was just going to spam everybody on their list anyway, so by that argument, this attack actually results in less spam all around!)

Except... perhaps an attacker could try the third type of attack, a phishing attack to get people's Netflix usernames and passwords, but not in order to compromise their Netflix account, rather to see if the person has an account with the same password at eBay or PayPal. Perhaps a user would be wary of a PayPal phish since they see so many of them, but they might fall for a Netflix one -- although then the attacker's success would be limited to people who had Netflix and PayPal accounts, and were using the same password for them both...

So it seems to me it's not obvious when this should be considered a problem. (All of the sites mentioned in this article were e-mailed about this issue months ago, and so far none of them considered it a serious enough threat to block all three of the avenues of attack listed above.) If abuse of this type becomes common, perhaps eventually these "queryable membership lists" will come to be considered in the same way as open mail relays -- which were never considered a glaring security hole, but were abused in ways that triggered a shift in people's thinking that got them to be gradually phased out, going from open relays being the default standard up to the early 90's, to the point where many ISPs today prohibit customers from running them. Maybe "queryable membership lists" will start to be abused more, if anti-spam technologies get smart enough that spammers can't send 1 million messages at a time any more and have to limit themselves to, say, 100,000 messages at a time to get through people's filters, so they have to pick which 100,000 of their addresses they could get the most value out of. Or maybe things will go in a completely different direction and this will never become a problem. I just think that, for now, we should be aware that some form of this trick works on the majority of sites that require an account, and the types of abuses described are at least possible.

Hmmmm

Not in their best interests, but they ARE capitolists.

Re:Not exactly

This is a completely invalid argument. Many companies realize their customers have no choice (save for litigation up through the supreme court via the clogged arteries of political and bureaucratic mayhem).

Think telecoms. I sign up for a service. I have to give a certain amount of information for service to my home of course as well as billing etc. Said company gets an enticing offer by a few marketing companies for their client list and any semblance of privacy has been taken from us without our consent, or deceptively with it, as consent was granted signing the contract for the service. Said consent was buried deep in the 6pt font on the back of Form B line 492.

How about credit card companies? Or major retail outlets? Many of these places offer reward cards or credit cards and the lists are sold off to other companies to use at their leisure. An old professor of mine used to have a Shopper's Drug Mart Optimum card. Shopper's Drug Mart is a massive chain in Canada (maybe in the US too?). Her son has a very rare disorder that requires a cocktail of drugs supplemented with high amounts of vitamin C. She started receiving snail mail spam regarding fresh fruit direct to her door as well as garbage mail from a competing pharmaceutical company regarding some meds. She only shopped at Shopper's and she always used her optimum points card. Outraged by this, she contacted the company who admitted that they do sell (or did at that time, about 10 years ago) their client lists to some "select and reputable companies."

Yeah sure right. They sell to whoever will pay large. When it comes to customer privacy, so long as the company realizes they have a stranglehold on a market, they can do what they want because either there is no competition, therefore no alternative for the consumer, or that their market dominance is such that even if they do lose a bunch of customers or have to deal with some legal issues, the benefits/profits far outweigh these marginal hiccups.

There are aspects of privacy one should not expect to retain (walking in public and not being noticed, or photographed etc) it is quite a different problem entirely when a company starts selling off or divulging information. Any of these releases of info should be opt-in only. Heck, in a lot of ways I believe a phone book should be the same way vs. paying to opt-out with an unlisted number.

Re:Not exactly

Good Luck with that. Go out and start a telecommunications company. Go find the venture capital, drop your own copper, your own fiber. Hire the lawyers needed to get the FCC to permit you to jump state borders. Oh, you can't find the 20 billion dollars this will require? But you stated that you could start a company that could offer the exact same service with privacy. No no you can't. This is exactly why these companies continue to exist today. They have bought their security. Laws are in place to protect them.

Now with something like a retail outlet, sure it is possible to overtake them, but if you start something in NYC and I'm in the middle of Arizona, it will take perhaps a decade or more before your mythical company can come and save me from the nasty retail overlords that dominate my realm.

You might be able to help out a few but the many would still be suffering. It will take a massive revolt the likes of the civil war to overturn all the laws that protect these gargantuan companies. So sure, the little companies abusing their customers may fizzle out, but the real abusers, the big bullies will just buy their way out of the mess.

Re:Not exactly

"Heck, in a lot of ways I believe a phone book should be the same way vs. paying to opt-out with an unlisted number."

Well, there is one way to almost get an unlisted number for free. You CAN tell them how you want your number listed. Say your name is Joe Franklin Sixpack. You can tell them you want it listed as J. F. or you can actually slide weird names by them occasionally (they do like to keep in similar to real name). Maybe do your name as J. Franklin, or F.Sixpack, or try to slip one like Francis S.....anyway, you can get away with this...they started doing it I think so single women wouldn't stand out so much in the phone books...but, you can pretty much choose what name is displayed with your name.

When I had a landline, and when I got a call asking for the 'weird name' I had listed in the phone book, I knew immediately that it was a marketer...and just told them wrong number, or that person had died or something....

Answer

If you are doing something you don't want to get caught for, use a throwaway email address. If you trust a web site to keep your information private, you need a reality check. You can fight the windmills all you want, but they will keep spinning away and ignore you.

Problem solved.

Re:Answer

Exactly. Even better, If you have your own domain name where all email gets delivered to one "catch all" makes it even easier. My friend uses a different email address for each site he signs up for to see who spams him or sells his email out. It's also a good way to know if a site is being honest with any policy where they state they won't do anything with your email address.

Additionally, it is a good idea to not use the exact same username for each site you have to "sign up" for, especially if you are unsure of the sites policies. The main problem for most folks is trying to remember all of this information when they want to log in. I've heard of devices that will help with this but have never tried them.

Re:Answer

Better yet, give such an email address to your girlfriend. This serves three purposes:

1. It's an email that only she uses, so you can sort it at top priority in your mail queue.
2. It's an email that only she uses, so she can't use it to find out if you are on any service.
3. It's an email that only she uses, so when you break up, you can delete the email address.

:-D

Besides, this whole question strikes of a very paranoid, insecure girlfriend. Maybe it's a sign that she's not worth holding onto. If I got caught with an account on match.com by a girl who were my girlfriend at the time, my gut reaction would be to ask "What kind of psycho nutjob are you?" followed by "Get the [expletive deleted] out of my house."

Also, an account on Match.com is a really bad example. Having an account doesn't tell you anything except that the person did at one time use said service. Asking if the guy created the account since [date relationship began] would be a more telling sign that the guy was unhappy in the relationship, but still would not be evidence of cheating. Evidence of cheating is... oh, I don't know, some other woman's undergarments under the couch cushion, another woman's hair in the shower drain, another woman's personal articles in the back seat of the car, etc., and even then, those can all be explained in other ways---a prior relationship, a next door neighbor doing bathroom remodeling, and taking your friend's daughter home from school because your friend was too busy/sick/abducted by aliens....

Short of catching the guy out with another woman, all you have is reasonable cause for suspicion, and girls, if you don't trust the guy you're with, you should break up with him. It really doesn't matter if your suspicions are confirmed or not unless you were friends before the relationship and hope to still be afterwards, but in that case, you wouldn't distrust the guy, would you? All that continuing a relationship built upon a lack of trust is going to do is eventually end in a divorce when that lack of trust turns into something nasty, either because you find out the guy really is cheating or because the guy finally gets sick of being treated like a criminal in his own home. Either way, it isn't a healthy relationship, and it is better to just get out the first time you think something might be wrong rather than going around acting like a psycho stalker. Here's a hint: normal guys really DON'T like that.... It's creepy.

The sites where membership would potentially be embarrassing (e.g. Playboy.com) would be expected to have much tighter limits on that sort of information, and would not be expected to give it out without significant proof that you are the account holder. I could be wrong, though. Might be worth testing just to find out. Volunteers?

Re:Answer

What worries me more, is that my mother, who is not my guardian anymore (by a longshot) can still call educational institutions that I attend and get information about my enrollment with nothing more than my name and social security number. She's hardly what anyone would call an expert in social engineering.

Even worse, places of prospective employment can call universities and get information about my enrollment as well (oftentimes without my social security number)! How many times have I lost a potential job from an employer who called a University to find out I never graduated. What a load! they should obviously by law only be allowed to take what I say about it.

Give me a break.

Re:Answer

Well I WAS using [e-mail], but fuck if I won't get spam now... Thanks a lot Slashdot!

Doh!

Sounds like Bennett's wife discovered his match.com account.

Re:Doh!

Actually, I got all confused from the title, because I'm like, ok, yeah I would feel guilty for invading his privacy.... wait, cheating? How would I be cheating for invading his privacy? AHH!!!!

Then I realized it's a slashdot article, and thus ignores my gender's existence.

Re:Doh!

Then I realized it's a slashdot article, and thus ignores my gender's existence

Ignore it? Hardly. We obsess over the existence of you gender endlessly. Problem is that we obsess over it in much the way we obsess over dragons, Bigfoot, UFOs, The Loch Ness Monster and other mythical creatures.

*looks through subscriptions*

Fuck.

If most spouses were savvy enough to call up sites and ask for information on their significant other, they probably would have caught them previously in some way, shape or form.

Chat logs, history and everything else, show quite a bit of information for any computer-literate person to evaluate.

Not only that, but I'm sure that anyone smart enough to hide everything and cover their trail, wouldn't leave personal information for their spouse to find.

need to check the regdate too

I hope you can get the registration date too, what if this person's girlfriend had a match.com account before he met her.

what if they met on match.com. but then she figured out he had two match.com accounts, like a secret one. then he would be cheating on her.

Seems to me...

...that if you are that paranoid, you should just use a different email address than the one known to your girlfriend. I just don't see this as a problem.

Re:Seems to me...

that if you are that paranoid, you should just use a different email address

Seems to me that if a society decides that paranoia is required in order to "earn" privacy, it should quit being surprised when it creates paranoid people.

Re:Seems to me...

Seems to me you should never give out your emmail address to your girlfriend, period. And why take any risks, don't even give them your number, or your real name for that matter. Personally I prefer to be extra careful about giving out personal information, I don't let them see my face or even let them know that we're dating.

It's going pretty well with my latest one I think. She's a bit shy though. Every time I call her it's nothing but awkward silences. Plus she's started closed the curtains :(

Re:Seems to me...

Dad ?

...thought it mattered

CT: We'd fix it if I CT: We'd fix it if I thought it mattered]]

Thought it mattered?!? I don't want people being able to find out that I'm a nerd!

...oh wait.

I can see it now...

Harold, I know... you've been on that Slashdot site again haven't you? Haven't you? Admit it!!!! You're fooling around with Ubuntu... behind my back!!!

Re:I can see it now...

Honey, no! I mistyped the URL for digg, I swear! You know I would never betray you and Gentoo...

Privacy on match.com?

Think about the purpose of that site for a second: the whole idea of match.com is you post a picture and a profile so you can meet new people. You're already spilling a ton of personally-identifiable information about yourself, and presumably someone is going to be able to search for you - so why get pissy about someone being able to determine that your e-mail address is registered there?

And while I'm thinking about it, if you're using match.com while you're already in a relationship with somebody then maybe you need to have a talk with that person and let them know things aren't working out.

Social Engineering

Amazing how much stuff you can get done by asking. A friend recently bought a new house. To shut off the power to his old house he simply called the power company and gave them his name and old address. No more power to that house. Of course names and addresses are usually a click away but I bet you already know the name of your neighbor who blasts music all night....

Login error notifications

So many sites out there tell you if you have got your email address or password wrong when you log in, when what it should do is tell you that your email OR password are incorrent. By entering someone elses email address (if used for login) into one of these sites, you can tell if they have registered or not.

Either you're together, or not, or you're open...

But if you're NOT "open", then think about your other half/significant other/whatever. If you're mutually apart for a period of time (a day, a week, whatever) then you've got a limited window. If you violate your other half, then you should have IN ADVANCE considered and expected to accept the consequences.

If Joe Blow gets caught, tough. If his girlfriend KNEW he was logging in to such sites, then she could live with it or walk away on her own. IF she finds out by other means, whatever they may be aside from personally breaking into his computer/s, then tough for him. Maybe people should mutually declare or assign a "sanctity rating" to their relationships so they can responsibly handle each others' emotions so no one is crushed when an occasional fling occurs.

Oh well, so many people are feeble-minded. And, DAMNED RUDE with others' feelings

Captch: "odorous"

an email address that's in use...

...should be considered public information. The street address comparison seems analogous here in many ways - just like anyone can see your address from the street, any time you use an e-mail address as a UID, it should be assumed that it's public. In other words, there should be no expectation on the part of someone sharing their address that it'll be kept secret.

I'm not saying this is a good thing (I think that, in general, sites that collect private information have at least an implicit responsibility to keep it private), but the bigger issue is that the average internet user needs to be aware of these really basic facts. Just like he/she needs to be skeptical enough not to click through to phishing attacks.

Until the state of awareness on these issues increases, there will always be opportunities for these sorts of marginal attacks on people's privacy.

Essay?

I don't know, but I'll be sure to let everyone know when I finish page 467 of the book you just wrote.

Proper password management

Many (most) email systems now will allow suffixed addresses, typically using "+" as the separator. Chances are that most of the services that use email address as a username or have the features that allow a third party to detect whether a particular email address is registered will treat "[e-mail]" as entirely distinct from "[e-mail]". So most people have easy access to throw away addresses. Unfortunately this doesn't fully solve the problem. Sites use email addresses as identifiers exactly because people remember their own. Using unique addresses for each service defeats that purpose.

The real solution to the real problem is for people to use proper username and password management tools. With such tools users don't have to remember their usernames and passwords, so schemes that try to verify whether a username is registered on a system won't identify to the world the person behind that username the way an email address might.

i am almost certain that:

Match.com and Yahoo's personals were both caught and fined for creating fake identities...

would you trust match.com and yahoo? not me...

Shame...

Big deal, an attacker can find out whether you're a Netflix user -- but that's not a huge privacy violation, it's not like I shamefully hide those red envelopes under my shirt while I'm scurrying back from the mailbox.

So here you are, making a big fuss about some perceived privacy problem. Yet appearantly privacy mainly means being able to hide the thing you are ashamed of. If that is all you are concerned with your privacy is not the problem.

So let me get this straight...

You want to be able to go get all the services you want while maintaining total privacy, huh? Well, if you want privacy, I have a 100% guaranteed-to-work solution for you. Don't give your email address out. Don't sign up for stuff on the web. If you're going to go in 'public', you're going to lose 'privacy', see, because they're opposites. That's how it works. You can go as emo about it as you want. It won't change the fact that in public, there is no expectation of privacy. (excepting that of your person, but that's not applicable online because you don't have an online 'body')

If you don't understand the system your either:

a. deserve to be caught
or
b. should not be fooling around

Not exactly the same thing, but I know a few married, computer-illiterate people who correspond daily with their fling using email. They think it is safe just because their local computer account is password protected. At the same time, their email program (OL, TB) is set to remember the password, and don't mind walking hand and hand with their fling down Broadway.

Why would you use match.com?

Okcupid is free and has some geek cred, it uses a least squares regression to match people.

And why would you use your regular email address? There is no anonymity on the Internet.

 

How much privacy should one expect?

As a practical matter, I have always assumed that anything that I submitted to a Web site was public, or close to being so. At most, it might be secured with what my grandfather called "the kind of locks that keep honest people out." After all, I chose to submit the information -- and if I were really paranoid, nothing forced me to tell the truth. The one obvious exception is payment data for E-commerce transactions, which I do think reputable sites (e.g., Amazon) take care over, despite a few highly-publicized lapses.

As far as a relationship goes, I would say that if the parties are fishing around for each others' correspondence and Internet accounts, the relationship already has some pretty serious problems with trust.

Don't use your personal email address!

It's simple really. Maintain 3 email addresses.

The first is your personal email address you give to friends and people who you actually want to communicate with.

The second is your 'account' address you give to companies, organisations, websites that you either have a financial arrangement with or some other connection that you actually care about.

The third is your 'trash & spam' address you give to websites/organisations that demand it, but you don't care about and never read.

I do this, and no person or organisation knows of the other. Not because it's a massive secret, but simply because they've no need to know. So in the scenario given here; my signup at Match would either be on my 'account' or 'trash & spam' email address and my girlfriend would only know my personal address.

Anyways, if I was the lying, cheating type, all I'd need to do would be tell the girlfriend that it was a ancient account I signed up to years ago and never use now.

Dump her!

I wouldn't want a girlfriend that would not trust me enough to ask me directly if I'm a match.com member. I would, of course, answer honestly.

If a girlfriend treats you with that much mistrust, you probably don't have a happy future together.

Article starts off with wild assumptions

"Suppose your girlfriend"....you can stop right there, buddy, this is slashdot!

An even simpler solution

I use an even simpler solution to the problem than any Mr. Hasselton suggests. Each site I sign up with where I care about this gets a unique e-mail address dedicated to them, one that isn't my regular e-mail address. I don't bother telling anyone else what these site-specific addresses are because nobody but that site should be sending mail to them anyway. Anyone checking my regular e-mail addresses would get back "not a member", since that address isn't a member. They can try and guess what different address I used, but that's only likely to work for sites like eBay where having an account isn't particularly embarrassing. For someplace like Match.com I'd be using something plausible but arbitrary like "tk487c5", and that's going to be all but impossible to guess if you don't know what it is already.

joeblow?

"I think my boyfriend might be cheating on me. His e-mail address is joeblow - at - aol - dot - com. Can you tell me if he's a member?"

Was the submitter really worried about poor [e-mail] being hounded by a spambot? I mean, his email address is [e-mail] for Christ's sake...

Slashdot is the most secure site out there

It is necessary to have a girlfriend (whatever that is) for this to be a problem, so I guess we are all safe...

Suspicious data

His argument that the requests would only be suspicious if the attacker is logged in misses some of the point. Let's say that Match.com usually gets 10 password requests per second, now they're suddenly getting an average of 15. That's a significant increase, so then they'll do some data mining or start requiring a Turing test. Also, his argument depends on not having to reuse any IP addresses, since the same IP address checking 3 email addresses that correspond to 3 unrelated accounts would be suspicious. I'm not saying that it's not harder to spot the attack when someone isn't logged in, but I am saying it's not impossible.

There are easier ways

One of the examples in the essay is that a girlfriend wants to know if her boyfriend is cheating on her... but by checking if he has an account?

Give me a break... First of all, what if he created the account several years ago and hasn't visited in that long? If the said girlfriend sees only that he has an account and automatically jumps to "He's cheating on me, the louse!" then I think they have some trust issues that go way deeper than Match.com.

Second of all, it's a social networking / matchmaking site. How difficult would it be to sign up for a freebie account and just search for his damn name? Seems to me like that would be a lot more definitive than checking the magic 8 ball of "Does he have an account?"

no data protection laws in the USA

This is big problem with data protection laws in the US. There's lots of complaints about this sort of thing from the EU, and some slow moves to sort it out.

But until you get decent DP laws there's little you can do...

More of a concern to me

I'm more concerned about a snot-nosed script-kiddie exploiting this. It's very easy:

1) Do as the poster suggests, and harvest a list of valid email addresses

2) Attempt to log on as those users (either by guessing that their username is probably the same as the username in their email address).

3) Repeat step 2 until the user account hits the "too many invalid login attempts" theshold, and gets locked out.

4) Repeat step 2 for every email address you have.

Voila. Service = denied. That user now has to go through the "reactivate my account" procedure, which probably involves several minutes of effort and possibly a Security Question that they might not remember. And if the script kiddie is doing his "job" right, that person will be locked out again by the next time they try to log in.

This can get annoying very quickly, especially on a time-sensitive site like eBay (where you are trying to win an auction), or even a stock-trading site.

Best Practices..

It has long been considered best practice to not identify that a user is valid in case of failure, as this can allow login harvesting. In case of privacy, I wouldn't necessarily disagree.

All your logins belong to us

Sorry

who gets to decide?

[CT: We'd fix it if I thought it mattered]

This is a perfect example of the heart of the privacy issue: who gets to decide what is and what is not a matter of privacy, what information is "worth" privacy protection, what circumstances warrant privacy, and what does not.

You can bet that the answer the vast majority of corporate America is going to respond with is "we do".

Other methods to get this information

One method that is incredibly difficult to stop -- at least, sites are unwilling to do so -- is through timing the login page. By timing how long it takes to respond to an invalid login attempt (just use a bogus password), you can figure out if the username/email is valid at that site. Check out the paper on this called Exposing Private Information by Timing Web Applications at http://www.abortz.net/ [abortz.net], which recently appeared at the IW3C2 World Wide Web conference this year.

Targeted Spam Lists? Why bother?

Spammers don't care how many of the people in their spam email lists are actually members of Match.com or wherever. What's the point of checking each of 100,000 emails against Match.com when a spammer can just send the same spam to all 100,000 and automatically get the ones that happen to both be members of Match.com and unlucky enough to be spammed by them?

tl;dr

Holy teal deer!

Could that article have been any longer?

Problem lies in a flawed assumtion

• Try to create a new account with that e-mail address. See if you get an error message saying the address is already associated with an account.
• Log in under an existing account, and try to switch to another e-mail address. See if you get an error message saying the address is already associated with an account.
• Use the forgot-your-password feature to request a password be sent to a given e-mail address. See if you get an error message saying that address is not associated with an account.

The first two points of the list are based on a very much flawed assumption by the applications, the problem to get a mail-address. The third is just plain stupid and leaks information.

Why are the first two flawed? They assume, that it is hard to get a second mail-address and therefore allowing only one account to be associated with an email-address somehow makes it harder for people to sign up multiple times. If that is not the reason, then the only other one I find is, to collect as many email-addresses as possible.

For me, there is no real reason, why an email-address can't be used multiple times. If you are afraid that someone signs up thousands of accounts, limit the number of signups per week. The probability that someone else trying to find out, if the address is being used hits one of the weeks where you signed up an account is much smaller.

Match.com have a duty to their shareholders.

1. Girlfriend finds out our victim is using Match.com
2. Girlfriend dumps our hero.
3. Hero must use dating agencies more to find new girlfriend.
4. Hero signs up for premium account, views more ads etc.

Clearly Match.com are doing what is their duty under capitalism!

Obligatory Business Plan

1) Get hold of the Goatse vistor's list.
2) Put it up for bid.
3) ????
4) Profit!

Mailman gets it right

Mailman gets it right while pointing out this vulnerability. Attempt to subscribe to a mailman listserv when you're already a member and you'll see no error page. Rather, the real subscriber gets an email with subject Mailman privacy alert that reads

An attempt was made to subscribe your address to the mailing list . You are already subscribed to this mailing list. Note that the list membership is not public, so it is possible that a bad person was trying to probe the list for its membership. This would be a privacy violation if we let them do this, but we didn't. If you submitted the subscription request and forgot that you were already subscribed to the list, then you can ignore this message. If you suspect that an attempt is being made to covertly discover whether you are a member of this list, and you are worried about your privacy, then feel free to send a message to the list administrator ...

Happens IRL, too

Hey, you don't need the internet to have companies f*ck with your privacy.

How would you like it if your hotel gave your room key to a guy with a bunch of TV cameras [youtube.com]?

- RG>

There's another angle to consider

If you were some sort of bottom-feeding scum with a big list of email addresses that you'd scraped from web pages - and looking to sell your list (profitable, and not risky) then you'd appreciate the difference between the price you'd get for raw addresses, or verified addresses.

Rather than launch a spam campaign and deal with the associated risks, why not just bounce your list off of a few high-traffic web sites to see if it's a valid login there? It's scriptable, doesn't cost anything - and the resulting list is much more valuable. If you're really lucky, the sites will offer other personal data as a "clue" to the forgotten password and you can plump up the list and make it even more valuable.

This is why Slashdot should care - if a login fails, no website should offer anything more than the fact that the login failed. No "bad password" or "invalid user id" - and definitely no "wrong password, click here and we'll ask you a personal question". Nothing more than "login failed".

More like how private AREN'T they.

I once googled myself. I got nothing, but my uncle turned up. I clicked on the link--it was an Asian board game association, and I am curious naturally--and found several thousand other names. Not just the names, either--full contact information, like addresses, phone numbers, e-mail, etc.

Third Party Discolsure? A corporate perspective

Working in a large corporation that has an extreme amount of exposure, I can't help but think that soon....very soon...these sites will more than likely get slapped with a lawsuit. Reading and agreeing to a privacy policy is one thing, but I would personally be EXTREMELY upset if anyone ever disclosed my email address to someone without proof of identity. Stalkers of the world unite! As long as you have an email address, your heart's desire is within reach. Leaving a voicemail with too much info can even be considered excessive and grounds for breach of contract. This will be an interesting topic to keep your eyes on.

ToSs it out

Does _anybody_ read the 4 or 5 page long Tos? And who has the time? There could be all kinds of nonsense in it! And for an experiment, probably the guys at Google might have already done this -> added terms like 'All my property will belong to Google after x time of having an account' in that huge document nobody cares to read.

EU Data protection law.

Interesting. I'd never considered that the use of e-mail addresses as a unique identifier caused information about a person to become publicly available, but it is pretty clear that it does.

I wonder how this sits with EU data protection laws, which make it illegal to reveal personal data about a third party as part of a business without that person's consent.

funny how the mind plays tricks

When I first read the excerpt in this article in the email digest, I read the example email address as [e-mail].

hundreds of paypal emails leaked

Hello, I received an email today that was supposed to have information about my account in it. It instead contained hundreds of usernames and or emails. I have contacted paypal about this but received no response. I am trying to get the word out where ever I can.

Re:anyone here use match.com?

Personally, I've been using Slashdot to meet my dating needs. Needless to say I have been less than impressed.

Mod Parent Down

For squirting spoilers into the text of his post. Jackass.

Re:Is privacy really a good thing though?

Is that village isolated from the outside world though?

There may be no crime perpetuated by the villagers themselves but what of visitors?

Re:Call me old-fashioned ...

You're a dolt. Adultery is NOT illegal in almost every county in the US. That, along with many other blue laws have been tossed out years ago. What contract did you sign when you got married? Most people only get a piece of paper stating that they are married.. there are no terms on it.

Re:Call me old-fashioned ...

While I wouldn't say that this guy had as yet done anything illegal (maybe slimy), you're right about privately owned web sites not having to respect one's right to privacy. Especially because in the USofA, there is no right to privacy. We have that expectation, but there is no constitutional right to it. This was hardly an issue when the constitution was written, but I think the time has come to address that.

Re:Call me old-fashioned ...

I believe a person's right to privacy ends when they're breaking the law -- adultery is still illegal last I checked

Maybe in some states, but last I checked it's not illegal in most states.

at least insofar as it's a violation of a marriage contract --

I don't know much about marriage law. But I've never heard of anyone being charged with a crime, at least in the last 30 odd years for committing adultery. I was under the impression most states had "no fault divorce laws" on the books many years ago.

or when their actions are causing harm to an innocent third party.

Wow, if "causing harm to an innocent third party" (assuming non-physical) is illegal, then can I put Rush Limbaugh in jail because he pisses me off?

Re:Call me old-fashioned ...

That is odd. I never signed a contract when I got married. If I was still married would I be arrested for not signing the "marriage contract"?

Just because something is illegal does not mean it is wrong. Just because it is wrong does not make it illegal. For example, it is illegal in the USA state of Georgia to have oral sex with your wife. At least it was in 1989 when James David Moseley went to prison for 17 months for going down on his wife. It was consensual. http://www.ling.upenn.edu/~kurisuto/sodomy.html [upenn.edu]

I have an open relationship. Each of us get to play with most anyone we want to. There are a few rules, but not many. In my world there isn't a lot of difference between "lying" and "cheating" in a relationship. They are both a violation of trust.

I don't have a lot of sympathy for a guy that is on match.com trying to "find someone the side", but only because he is trying to hide it. To me that is also a violation of trust.

Re:Call me old-fashioned ...

Wow, a lot of the responders were kind of beside the point, so let me sort through:

-No, there isn't necessarily a "marriage contract".
-But, the law typically is specified so that by getting married, certain obligations attach.
-Yes, adultery is legal in some places, BUT not others
-Breach of contract isn't the same thing as breaking a law.
-But, the website will typically have a policy against married users signing up.
-But, and this is the most important, just because someone claims they're married to a user and want you to share information, doesn't mean you should believe them and comply. That was the point all along! There are proper channels to go through, and the site should give that level of information that easily.

Re:Call me old-fashioned ...

I believe a person's right to privacy ends when they're breaking the law -- adultery is still illegal last I checked, at least insofar as it's a violation of a marriage contract -- or when their actions are causing harm to an innocent third party.

From the statement, I guessed that you were female. Most females I know seem to think that adultery is illegal or if it is not, that it should be.

Sorry Jennifer, it is not illegal. I thought pagans enjoyed a verity of non-standard living arrangements... Polygamy, etc.

The problem is that there is little to no privacy and few really understand that.

Re:Call me old-fashioned ...

I am not a lawyer, and I have not researched the laws of all 50 states. I do know that in my county an individual was recently sued for "Alienation of Affections." The defendant lost the case. I can't remember if the defendant had to pay damages or, if so, what the damages were. I am not aware of a criminal penalty for adultery where I live, but it seems there is a civil liability for the person who instigates the breakup of a marriage.

Re:Is privacy really a good thing though?

"I like the idea of a Panopticon style world actually, with no privacy at all."

Are you serious? First sentence in the article: "The Panopticon is a type of prison building . . . " Which is exactly what a world without privacy would be.

"May your chains set lightly upon you, and may posterity forget that ye were our country[man]."
Samuel Adams

Re:Oh pfeh.

You don't even have to ask most sites. Just punch in the person's email address in the "forgot password" form page and see if it corresponds to a registered member's email address. If it's not in the database, you'll get an error. If it is, they'll get a reset password email that they never requested.

Try reading TFA. He not only covers this attack - he discusses it's drawbacks.

Re:Call me old-fashioned ...

What contract would this be? You don't sign anything that says you will be sexually faithful to your spouse. In fact, some marriages allow this activity. There is nothing illegal about it. Immoral, sure...but if this were a law, why would Clinton still be running free or without a fine?

Re:Saved By The Force

(1) you need to know someone's date of birth (this is a really good idea actually).

If you're worried that your partner is cheating on you, and you don't know their date of birth, I'd also be questioning your commitment to the relationship.

Re:Is privacy really a good thing though?

oh my god that is so scary!

People, by simple human nature, are irrationally judgemental.

Given omniscience, most people will seek to place themselves above the people they observe, on a moral scale and will seek out faults with their behavior.

Given that the total lack of privacy is associated with all sorts of serious psychological and developmental problems, it seems a profoundly bad idea.

Lack of crime is not indicative of a healthy society. It may be one small metric, but personal happiness is better obtained through liberty, freedom and privacy at the expense of saftey. I think the ideal is a balance point in the middle.

I think our culture is already swaying too far into the 'nanny state' and the UK has gone even further, to the point that most people fear the police on instinct and mistrust their neighbors in a way that would have seemed absurd 50 years ago.

On the other hand, the utter anonymity of a huge city does cause people to grow antisocial.

So here are the two hands.

1) A totally anonymous person has no reason other than internal fortitude, to have any morals. Having a sense of responsibility for oneself is a stabilizing force.

2) A person totally lacking privacy and anonymity has no individualism, other than that which is granted to him by the watchers, which leads to all sorts of crazy dissociative personality disorders, etc.

Surely there is a balance, right?

Panopticon.... sheesh

Stew

Re:Is privacy really a good thing though?

Your Dad isn't Patrick McGoohan, is he?

Re:Is privacy really a good thing though?

It also would have no real freedom to do things which are legal but enough out of the mainstream to cause significant problems if your neighbors and family knows. Depending on where you live, that can be anything from being a member of a fringe political group to sexual preferences.

Re:disposable web mail

If you can't be bothered to spend the time on creating a disposable Yahoo, Gmail, Hotmail or whatever then you should get caught. That is like robbing a liquor store with your name and address printed on the back of your shirt. Even the dateline predators created new accounts like "[e-mail]" or whatever.

Tobias: No, no, it's pronounced 'a-NAL-ra-pist'.
Buster: It wasn't really the pronunciation that bothered me.