An anonymous reader quotes a report from Help Net Security:"Based on tracking cookies, the transaction can be linked to the user's activities across the web. And based on well-known Bitcoin address clustering techniques, it can be linked to their other Bitcoin transactions," they noted. "We show that a small amount of additional information, namely that two (or more) transactions were made by the same entity, is sufficient to undo the effect of mixing. While such auxiliary information is available to many potential entities -- merchants, other counterparties such as websites that accept donations, intermediaries such as payment processors, and potentially network eavesdroppers -- web trackers are in the ideal position to carry out this attack," they pointed out.