writes ""It should come as no surprise to Bitcoin users that despite the pseudonymity the cryptocurrency offers, its transactions can be tracked. But University of California at San Diego researcher Sarah Meiklejohn proved that privacy problem more clearly than ever by showing a reporter that she could detect a specific point in Bitcoin's blockchain record of transactions where he had spent Bitcoins in exchange for marijuana on the Silk Road, the most popular online Bitcoin-based black market for drugs.
To simulate a law enforcement subpoena, the reporter for Forbes began by giving Meiklejohn a Bitcoin address associated with Forbes' account. But with just that information, Meiklejohn was able to draw on a "clustering" analysis she had performed to identify Silk Road addresses and match them with the one used in the .3 BTC drug buy. She admits that a user who took more efforts to obscure his or her Bitcoin address through a laundering service or other unidentified Bitcoin wallets would be harder to track.""Link to Original Source