CacheLogic, a UK network equipment maker, reported that BitTorrent has now superseded FastTrack -- which is used by Kazaa -- as the most popular P2P client worldwide. CacheLogic estimates that there are always at least 10 million people logged on to a P2P network at any time.
The company also said that the vast majority of P2P traffic came from files in excess of 100MB.
Many of these are likely to be copies of films, with CacheLogic reporting that 30 percent of P2P traffic for one ISP was all from a single 600MB file, which they suspect was a copy of a major film that had just been released.
Andrew Parker, CacheLogic's founder and chief technology officer, told ZDNet UK that P2P traffic is continuing to grow.
Because some P2P applications now use dynamic or variable network ports, even using ports used for other applications such as email and Web traffic (ports 25 and 80 respectively), it can be almost impossible for ISPs to block them, Parker said.
This also means that the true extent of P2P traffic isn't always obvious even to ISPs, Parker added.
CacheLogic reached these conclusions after spending six months monitoring the networks of several ISPs with a new product called Streamsight 510. This device can be placed in a local telephone exchange or other regional point of presence, to perform deep-level packet inspection of an ISP's network traffic. Streamsight 510 goes on sale to ISPs later this year.
According to Parker, BitTorrent's is particularly dominant in the Asian market, where it is used by Web users to access video files.
Last week the Motion Picture Association of America (MPAA) released a report claiming that one in four people have illegally downloaded a film from the Internet. The validity of this report has subsequently been called into question, though, with some critics pointing out that only broadband users were surveyed.
CacheLogic says that much P2P traffic is legitimate, pointing out that BitTorrent is also used to share content such as the Fedora Linux distribution. It estimates that the total cost of P2P is more than €500m per year.