On July 4 2014 we found a group of relays that we assume were trying to deanonymize users. They appear to have been targeting people who operate or access Tor hidden services. The attack involved modifying Tor protocol headers to do traffic confirmation attacks. The attacking relays joined the network on January 30 2014, and we removed them from the network on July 4. While we don't know when they started doing the attack, users who operated or accessed hidden services from early February through July 4 should assume they were affected. Unfortunately, it's still unclear what "affected" includes. // http://www.theverge.com/2014/7/30/5951479/tor-says-unknown-attackers-compromised-hidden-services Who was behind the attack? The Tor team suspects the CERT division of Carnegie Mellon University's Software Engineering Institute (SEI). Earlier this month, CERT abruptly canceled a Black Hat conference talk called "You Don't Have to be the NSA to Break Tor: Deanonymizing Users on a Budget." The NSA has famously attempted to break Tor, to limited success.