Bitcoin has always been a popular choice with black marketplaces far before Bitcoin was popular (think SR and the like), and only became more popular as Liberty

Bitcoin has always been a popular choice with black marketplaces far before Bitcoin was popular (think SR and the like), and only became more popular as LibertyReserve fell over. However it isn't really used as a currency, and more as a transport mechanism for cash (seeing how Bitcoin isn't anonymous at all, I'd imagine the strongest reason for these guys to use bitcoin is you can't chargeback with bitcoin)