jfruh writes "One of the great attractions of Bitcoin as a currency is that it's completely secure and anonymous. But according to researchers (PDF) from UC San Diego and George Mason University, that anonymity starts to vanish the minute you exchange bitcoin for real-world items or conventional currencies. The researchers tracked transactions across the Bitcoin ecosystem and found points where it would be easy for a government with subpeona power to find the identity of a Bitcoin user. They also concluded that the currency wasn't especially attractive for money-laundering purposes."
Graph theory explains many things.