Blockchain.info has a taint analysis tool, and there are other tools. Most bitcoins have a long, highly-mixed history, tainted some small fractional percent of

Blockchain.info has a taint analysis tool, and there are other tools. Most bitcoins have a long, highly-mixed history, tainted some small fractional percent of most any address from time before. Probably because mtgox, as the largest exchange, mixes coins pretty thoroughly. Risk to the thieves is that if they try to sell the coins through them, mtgox will freeze the funds. They have to be mixed elsewhere first and who knows what taint threshold mtgox uses to freeze funds. For example, after the Linode hack the stolen coins were moving around and there were reports, from people who had bought coins from cryptoXchange or had paid with paxum, that mtgox was freezing those deposits because they were connected to the stolen funds.