We reported last Tuesday that some malicious code was found that exploits a vulnerability in Firefox, and is used to snoop on Tor users. All evidence says that the exploit was developed and deployed by U.S. government contractors for the NSA.
From IT World:
The TOR Project is advising that people stop using Windows after the discovery of a startling vulnerability in Firefox that undermined the main advantages of the privacy-centered network.If you haven't switched to Linux yet I recommend doing so now. If you didn't know, I have my own flavor of Linux called Bauer-Puntu Linux that has many anti-government encryption and security tools installed by default to protect your privacy.
"Really, switching away from Windows is probably a good security move for many reasons," according to a security advisory posted Monday by The TOR Project.
People using Linux and OS X were not affected, but that doesn't mean they couldn't be targeted in the future. "This wasn't the first Firefox vulnerability, nor will it be the last," The TOR Project warned.