Researchers have uncovered more evidence that the TOR anonymiser network is being misused by hackers, and quite likely government intelligence agencies.

TOR (The Onion Router) is a network of proxy nodes set up to provide some privacy and anonymity to its users. Originally backed by the US Naval Research Laboratory, TOR became an Electronic Frontier Foundation (EFF) project three years ago. The system provides a way for whistleblowers and human rights workers to exchange information with journalists, among other things. The system also provides plenty of scope for mischief.

The presence of rogue nodes on the network was recently highlighted by security researcher Dan Egerstad, who controversially posted details of login credentials of about 1,000 email addresses, including at least 100 accounts belonging to foreign embassies, obtained by listening to traffic passing through five exit nodes under his control. Abuse of the system is far from isolated, other research suggests.

Members of the Teamfurry community discovered TOR exit-nodes that only forwards traffic association with ports used for unencrypted versions of protocols including IMAP and POP email (TCP ports 143 and 110), and IM traffic. Other nodes only relay traffic associated with MySpace or Google searches. The malign purposes behind such a system are fairly easy to guess, while their legitimate use is far trickier to imagine.

"Even though just a suspicious configuration isn’t enough to tag an exit-node evil, I wouldn’t touch these with a ten-foot long toothpick," Teamfurry warns.

Another Tor exit node used fake SSL certificates to run man-in-the-middle phishing attacks. Information on the rogue node was forwarded to German authorities, who moved quickly to take down the node. The node was the only one of 400 nodes tested that was running man-in-the-middle attacks, but as net security firm F-Secure notes, it "only takes one".

TOR is set up such that users have little or no idea who controls the exit nodes their data passes through. For this reason encrypting sensitive traffic sent over the network is the first, but not the only, security precaution for using the network. ®