File sharers who download torrents from services such as The Pirate Bay can expect to find their IP address logged by copyright enforcers within three hours, according to a new study by computer scientists.

Researchers at the UK's University of Birmingham reached the finding at the end of a two-year study into how organisations are monitoring illegal file sharers.

They conclude that large scale monitoring of the most popular illegal downloads from The Pirate Bay has been taking place over the last three years. On average an illegal file sharer, using BitTorrent to download the most popular content, will be picked up and logged within three hours of starting a download. Downloads of more popular files tend to be picked up more quickly, as the paper explains.

Average time before monitors connect: 40% of the monitors that communicated with our clients made their initial connection within 3 hours of the client joining the swarm; the slowest monitor took 33 hours to make its first connection. The average time decreases for torrents appearing higher in the Top 100, implying that enforcement agencies allocate resources according to the popularity of the content they monitor.

"The monitors we detected don't actually collect any parts of the file from the alleged uploader, therefore the evidence of illegal file sharing collected by monitors may not stand up in court," Tom Chothia, one of the four researchers along with Marco Cova, Chris Novakovic and Camilo Gonzalez Toro, told El Reg.

"We found six very large scale monitors, however all of them where using third-party hosting companies. Therefore we can't be sure who they really were, or if they where monitoring for legal or for marketing purposes. We also found a further seven small scale monitors that included some security companies, hosting companies and a research lab," Chothia added.

Copyright holders carry out monitoring on file-sharing networks using two approaches: indirect monitoring, where the presence in of an IP address in a peer list of a tracker is logged, or direct monitoring, where attempts are made to download files from IP address listed in Torrent swarms are actually listed. The Birmingham researchers found that direct monitoring is happening but that indirect monitoring remains by far the most common technique applied by copyright enforcers.

A technical paper, The Unbearable Lightness of Monitoring: Direct Monitoring in BitTorrent, describing the Birmingham team's research can be found here (PDF).

The paper, more aimed at anti-piracy officers at ISPs and copyright enforcers than end-users, was presented at the SecureComm conference in Padua, Italy yesterday. ®