It should be no surprise that file-sharing services like BitTorrent are monitored for illegal activity, but just how aggressive is the tracking? A new report from U.K. researchers found that monitoring can begin within hours.

"On average an illegal file sharer, using BitTorrent to download the most popular content, will be connected to and have their IP address logged within 3 hours of starting a download," according to computer scientists from England's University of Birmingham.

The researchers developed software that acted like a BitTorrent client and then kept track of any connections made to that software. About 40 percent of connections were made within three hours of the university software logging in; the slowest monitor took 33 hours.

"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," researchers said.

The report said that "massive monitoring" of the most popular file-sharing services, like The Pirate Bay, has been going on for the last three years. Haphazard collection methods, however, often means that much of the data is inadmissable in court. For example, monitors frequently connected to the university's software to verify activity, but didn't actually collect any of the files being shared.

"Therefore, it is questionable whether the monitors observed would actually have evidence of file sharing that would stand up in court," researcher Dr. Tom Chothia said in a statement.

The report said that the big monitors usually hide their identities via third-party hosting companies. This can allow them to avoid "block lists" that try to stop their activity. Researchers were, however, able to identify copyright enforcement organizations, security companies, and government research labs as some of the groups that were monitoring file-sharing activity.

"This work reveals the full scale of the monitoring of illegal file sharers," Chothia continued. "Almost everyone that shares popular films and music illegally will be connected to by a monitor and will have their IP address logged. What is done with this information in the long term only time will tell."

Researchers presented their findings today at the SecureComm Conference in Padua.