The Russian Ministry of Internal Affairs recently announced a contest to create a method to identify Tor users, with a prize of about $114,000.
Clearly the government is worried about the ability of Tor to allow people to bypass the increasingly draconian Internet laws that have been put in place. This puts a big target on Tor, but people have been working on breaking Tor for years. This year a talk at Black Hat on cracking Tor anonymity was pulled without explanation after it was announced and scheduled.
Being free and well established, Tor has the largest user base of any privacy service, so it is the obvious first target. Its distributed design also introduces paths for attack not available in other designs like Anonymizer Universal.
It will be interesting to see if this move drives Tor users to other services, and whether that in turn leads to expanded efforts to crack those tools.