[grrowl]

In August 2013, the FBI injected a Javascript exploit with a MITM attack to uncloak the real IP addresses of people accessing Silk Road over Tor: http://arstechnica.com/security/2013/08/attackers-wield-fire...

[edit] Nerdier link with exploit demo: http://resources.infosecinstitute.com/fbi-tor-exploit/