An anonymous reader writes "Darren Nix works for 42Floors, a business that uses its website to help people find office space. He recently received a marketing email for a service that offered to identify visitors to his website. After squeezing some information out of the marketer and playing around with a demo account, he now explains exactly how sketchy companies track your presence across multiple websites. The marketer offered to provide Nix with 'tracking code that would sit in your web site' which would 'grab a few key pieces of data from each visitor.' This includes IP addresses and search engine data. The marketer's company would then automatically analyze the data to try to identify the user and send back whatever personal information they've collected on that user from different websites. Thus, it's entirely possible for a site to know your name, email address, and company on your very first visit, and without any interaction on your part. Nix writes, 'A real-world analogue would be this scenario: You drive to Home Depot and walk in. Closed-circuit cameras match your face against a database of every shopper that has used a credit card at Walmart or Target and identifies you by name, address, and phone. If you happen to walk out the front door without buying anything your phone buzzes with a text message from Home Depot offering you a 10% discount good for the next hour. Farfetched? I don't think so. ... All the necessary pieces already exist, they just haven't been combined yet.'"