updated 10:49 pm EDT, Mon August 5, 2013
Malware collects data about Tor users, forwards to FBI contractor
According to security researcher Brian Krebs, "Tor software protects users by bouncing their communications across a distributed network of relays run by volunteers all around the world. As the Tor homepage notes, it prevents anyone who might be watching your Internet connection from learning what sites you visit, it prevents the sites you visit from learning your physical location, and it lets users access sites that are blocked by Internet censors."
Freedom Hosting, before its takedown, was the host for some of the Tor network's highest-traffic sites, including TorMail and the Hidden Wiki. Every site hosted by Freedom Hosting became inaccessible around 6:40AM EST on August 4.
The Tor browser is based on Firefox 17. The current version of Firefox, version 22, is not susceptible to the vulnerability.