The "sites" keep track of the transactions. This information could leak or law enforcement could successfully request this information. High level analysis cou

The "sites" keep track of the transactions. This information could leak or law enforcement could successfully request this information. High level analysis could find btc-altcoin transactions that "fit" together, maybe with later transaction when the person will eventually cash out, and use other data thats not obvious to us right now. A difficult problem, but one that is straightforward, fashionable (big data), profitable (lots of money at stake), and potentially something that law enforcement/intelligence agencies work on. We tend to underestimate future capabilities ;)