Just 100 peer-to-peer users upload 66% of all content found on the top two BitTorrent portals. That content, in turn, comprises 75% of all files downloaded by P2P users.

That's the surprise finding of research presented in late 2010 at the ACM International Conference on Emerging Networking Experiments and Technologies in Philadelphia, by researchers from Carlos III University in Madrid, IMDEA Networks Institute, the University of Oregon, and the Technical University of Darmstadt in Germany.

The research team examined 55,000 files being hosted on Mininova and The Pirate Bay -- the two main portals for files being hosted on the BitTorrent P2P network. What they found was that just two groups of users were responsible for the majority of uploads.

The first group, which they dubbed "fake publishers," generated an enormous number of fake files. These they traced to two sources: organizations working on behalf of copyright holders who flooded BitTorrent with fake files in a battle against people seeking to download copyrighted material; and attackers, who unloaded large quantities of malware disguised as in-demand content or applications.

But the other group of users -- numbering only about 100 people -- uploaded real files that would then be downloaded by tens of thousands of BitTorrent users. Most often, these files were new films or recent television series episodes.

Why did they share content, especially given the legal risk? That was the big question posed by the researchers: Is file-sharing done primarily for altruistic reasons, or in the pursuit of profit?

The answer was profit. "The success of BitTorrent is due to the fact that a few users make a large number of [files] available in exchange for receiving economic benefits," the researchers said. Primarily, those benefits accrue from online advertising, followed by VIP services that allow subscribers to download BitTorrent content more quickly.

Tying only about 100 users to 75% of all downloaded P2P files -- at least some of which contain copyrighted material -- means that copyright holders might consider how to create disincentives aimed just at this group, said researchers. "If these users lose interest in this activity or are eliminated from the system, BitTorrent's traffic will be drastically reduced," they said.

Attend an all-day virtual event from InformationWeek and Dark Reading on finding and fixing the security holes in your enterprise. It happens Feb. 3. Find out more. (Free registration required.)