Researchers have devised a way to monitor BitTorrent users over long stretches of time, a feat that allows them to map the internet addresses of individuals and track the content they are sending and receiving.

In a paper presented earlier this week at the Usenix Workshop on Large-Scale Exploits and Emergent Threats, the researchers demonstrated how they used the technique to continuously spy on BitTorrent users for 103 days. They collected 148 million IP addresses and identified 2 billion copies of downloads, many of them copyrighted.

The researchers, from the French National Institute for Research in Computer Science and Control, also identified the IP addresses where much of the content originated. They discovered the the vast majority of the material on BitTorrent started with a relatively small number of individuals.

"We do not claim that it is easy to stop those content providers from injecting content into BitTorrent," they wrote. "However, it is striking that such a small number of content providers triggers billions of downloads. Therefore, it is surprising that the anti-piracy groups try to stop millions of downloaders instead of a handful of content providers."

The researchers said the information leak is built in to the very core of most BitTorrent systems, including those used by ThePirateBay and IsoHunt. They support commands such as "scrape-all" and "announce started/stopped," which when used repeatedly can be used to identify the IP addresses where content originates or is being distributed once it has proliferated.

By collecting more than 1.4 million unique .torrent files, they were able to identify specific pieces of content being distributed by particular IP addresses. The results are about 70 percent accurate.

"At any moment in time for 103 days, we were spying on the distribution of between 500 and 750K contents," they wrote. "In total, we collected 148M IP addresses distributing 1.2M contents, which represents 2 billion copies of content."

The insecurities baked into BitTorrent allowed the researchers to discover IP addresses even when they were hidden behind the Tor anonymity service. It should be pointed out that this isn't the fault of Tor, which has long urged people to refrain from using BitTorrent over the virtual privacy tunnels. In light of the new research, project managers renewed that admonition on Thursday.

"The BitTorrent protocol is vulnerable to tampering by malicious parties," Jacob Appelbaum, a full-time developer for Tor volunteer wrote in an email to El Reg. "This is not so different than when you're using Tor or on any other internet connection. If someone wants to tamper, there's nothing in the protocol to stop the tampering."

A PDF of the paper is here. ®