[kropotkin]

This particular attack exploits a known issue of Tor, which has existed by design since day one.

Just so everyone's clear, this was not a "known issue of Tor". It was a javascript based Firefox exploit.

[enneff]

The known issue of Tor that I refer to (and sorry for not being more specific) is that a buggy client can leak your identity. The Firefox exploit leverages this design weakness.