ONE of the advantages of Bitcoin—a cryptographic currency popular on the internet—is its anonymity. That means that, although it has plenty of legitimate uses, it is also the favoured scrip of those who wish to buy drugs from sites like the Silk Road, or keep their transactions away from the watchful eyes of the taxman.
Now, though, in a paper due to be presented next month at the Internet Measurement Conference in Barcelona, Sarah Meiklejohn of the University of California at San Diego and her colleagues argue that Bitcoin may not be quite as private as had been assumed. The fact that many Bitcoin users want to convert their digital currencies into the more traditional sort, and the fact that most transactions now pass among a handful of major exchanges and electronic wallets, mean that it is possible to track the movements of large numbers of Bitcoins. Ms Meiklejohn says that the details aren't enough, by themselves, to identify users. But they could conceivably provide the police with enough information to obtain subpoenas and would reveal who owns an account associated with a transaction.