On August 19, a twentysomething man who goes by the online handle ZachXBT was walking into an airport to board a flight home—which airport, his real name, where home is, he’d rather not say—when he saw an alert on his phone. A sum of bitcoins had just been transferred to a small cryptocurrency exchange, one of many whose transactions he constantly monitors on Bitcoin’s blockchain for signs of criminal money laundering.

Source: Wired – Threat Level