More sophisticated criminals use obfuscation methods that make it very hard to be tracked down. One of the most basic ones is a technique known as "chain-hopping", whereby money is moved from one cryptocurrency into another, across digital currency exchanges - the less-regulated the better - to create a money trail that is almost impossible to track. Newer and more complex money-laundering methods have also emerged in recent years, which make it very difficult for law enforcement and bitcoin security firms such as Elliptic or New-York-based Chainalysis to track down cybercriminals. "It’s a cat-and-mouse game – as police and companies like Elliptic catch up to criminals’ techniques, they invent new techniques," said Jerry Brito, executive director of the Washington, D.C.-based Coin Center, a not-for-profit advocacy group focusing on public policy issues around cryptocurrency.

http://www.reuters.com/article/us-cyber-attack-bitcoin-idUSKCN18E2F1