Most file-sharing programs aren't the most upstanding citizens of the computing world. Yes, the entertainment industry hates them for the way they're used to download movies and albums without paying -- but many of these programs also fail to treat their own users well, often installing an unadvertised, unwanted load of advertising and spyware.
BitTorrent is different. This free, open-source program offers a spyware- and nuisance-free installation. And while it is certainly handy for downloading movies and other copyrighted material for free, it's also increasingly used to distribute software and entertainment legally.
This makes BitTorrent (www.bittorrent.com) not only a fascinating test case for legal experts, but it also looks a lot like the logical fusion of peer-to-peer file-sharing and traditional downloading. It's too robust to stamp out with lawsuits, but too effective not to adopt for commercial use.
BitTorrent works by enlisting everybody into the file-distribution process. A BitTorrent download starts when you click on a ".torrent" link on a Web page, in an e-mail or some other document. That link gets handed off to your BitTorrent program, which follows that link to a "tracker" computer. (BitTorrent doesn't have any file-search capability built in; you must find these .torrent links yourself.)
The tracker, in turn, points your copy of BitTorrent to a random grouping of other BitTorrent users who have the file you want. Your copy then starts downloading, assembling all these disparate chunks into a perfect copy of the original. But once you have part of the file on your computer, BitTorrent also begins uploading that to other people who come looking for it.
This uploading continues until you close the BitTorrent program.
The net effect of this is a vast increase in the resources available to distribute a file -- instead of the limit being one Web site's own Internet connection, you can theoretically put the entire bandwidth of the Internet to work. The original distributor of the file needs to upload it only once, after which everybody else takes care of the work -- and as more people download it, the torrent picks up speed.
This approach is overkill for a three-minute song, but for a 30-minute sitcom or a two-hour movie, it's highly effective.
As a result, the Motion Picture Association of America is less than thrilled about that particular use. It has taken tracker sites to court for their role in pointing users to movie downloads. As part of one settlement, it took over one such site, LokiTorrent.com, and turned it into an online billboard warning users of the legal risks they faced.
But the Washington-based lobby hasn't sued BitTorrent's developer, Bram Cohen of Bellevue, Wash., nor has it gone after individual BitTorrent users. (Full disclosure: For research purposes, I've used BitTorrent to grab two episodes of "The Simpsons" and Jon Stewart's famously combative "Crossfire" appearance.)