There are three relevant hacks here, and it's good to keep them clearly separated. First, Anonymous hacked into some server which ran a lot of hidden services

There are three relevant hacks here, and it's good to keep them clearly separated. First, Anonymous hacked into some server which ran a lot of hidden services (essentially, Tor was used to hide the identity of the server.) Some pedophiles were exposed, etc. This is not an attack on Tor: vulnerable webapps can be hacked, hidden service or not. Second, it's been known for a long time that wide-scale traffic analysis can be used to discover who's talking to who. E.g. if I send packets into Tor at t=0, t=.1354 and t=.1432 and you receive packets from Tor at t=1.832, t=1.982 and t=2.091, these may well be related - the delay is approximately constant. (More clever analysis gets you better results.) This is a known attack and not fixable without introducing big random delays. (Mixmaster, "Tor for e-mail", does introduce such delays. It's not a good fit for the web, though.) Third, some Eric Filiol reportedly claims to be able to decrypt Tor traffic (by hacking into lots of vulnerable Tor nodes and overloading the unhackable ones to force traffic through the compromised nodes.) This seems unlikely: the report seems to have lots of (minor) errors, and the description of the attack makes no sense (controlling the flow of encrypted data does not let you decrypt said data.) It is possible to discover who's talking to who if you hack into a sufficient number of nodes, by using the nodes as network monitoring stations. However, that's essentially the same hack as #2 above. (Note that only the last node in the Tor network to see the packet has access to the unencrypted form. Since running a Tor endpoint invites lots of unwelcome attention, these are probably far more professionally run than the average node.)