The Motion Picture Association of America and its counterparts in the music world want to shut down illegal traffic in copyrighted material. But at the same time, they're desperate to find ways to make money out of a technology so ingenious that its legal uses in distributing information are burgeoning.

Consider just two recent stories. The widely hyped Star Wars film "Revenge of the Sith" appeared on the Internet as an illegal file download on the same day it opened in theaters. To get it, users resorted to the BitTorrent file-sharing network, a new technology that makes it easier than ever to download extremely large files. The MPAA has, in the past, gone after Web sites that provide "tracker" links for BitTorrent, needed to make the file distribution work.

But just this April, Vinton Cerf, author of the TCP/IP protocols that are at the backbone of the Internet, told an Internet roundtable in Australia that he had spoken to several movie producers about using BitTorrent to move content to end users. And why not? Files don't care how they arrive on your system, but arm a PC with a decent home network and you can play back a downloaded movie on your digital video recorder. Shouldn't Hollywood want a piece of that action, bypassing all those pesky video dealers?

BitTorrent is an interesting story in and of itself. The work of networking guru Bram Cohen, it was designed to make each file, in effect, its own "network." To download a particular file, you first download a "torrent" file, usually found on a Web site; this contains the address of a tracker server that carries information about where the file is located and who is downloading or uploading it.

As your own download takes place, your PC simultaneously uploads the same file to other users. The bandwidth is thus distributed among those who are downloading and uploading the file. An unusual advantage is that the more popular a file is, the faster the download.

And yes, some uses of BitTorrent are clearly illegal. Consider Australia, where impatient TV viewers have been downloading the latest shows from the United States. It turns out that Australia is the second-largest downloader of pirated TV on the planet, second only to the United Kingdom (the U.S. is third), and BitTorrent seems to account for 70 percent of these illegal downloads.

Indeed, in December the MPAA started a series of actions against BitTorrent tracker sites. Some of the biggest sites disappeared, and the MPAA warned that it had filed suits against BitTorrent tracker operators in several countries, and would continue to put legal pressure on anyone using the network for illegal copyrighted material. As if to counter such moves, BitTorrent's new beta version has been built to eliminate the need for tracker sites.

But is BitTorrent to blame or those who use its ingenious technology for dubious purposes? As Hollywood clearly recognizes, there are many ways that moving big files legally makes sense. Numerous Linux companies make their products available to subscribers via BitTorrent download. Indeed, it's a no-brainer: The customers become the ones who make the distribution mechanism possible.

Game publishers like BitTorrent for the same reasons, and I suspect it will emerge as the standard way to download large programs. The copyright war, then, is only part of the BitTorrent story.

Next up for Cohen is a search tool, now available at the BitTorrent site. No doubt the MPAA and other content guardians will use it to track down illegal file downloads, a reminder that technology sometimes solves the very problems it helped to create.