Traffic Analysis allows to reveal majority of users on Tor Network Posted by ebauch on Monday November 17, 2014 @01:03PM from the openrev.org dept. http://www.openrev.org/paper/on-the-effectiveness-of-traffic-analysis-against-anonymity-networks-using-flow-records ( 2 comments | 3 points | on HN )
It's an active attack, meaning it requires packet modification. Its been done to death, see stream watermarking, etc.
Show me an effective passive attack with a powerful but non-global adversary and I'll be impressed.