Issue 13.01 - January 2005 Subscribe to WIRED magazine and receive a FREE gift!

"That was a bad move," Bram Cohen tells me. We're huddled over a table in his Bellevue, Washington, house playing a board game called Amazons. Cohen picked it up two weeks ago and has already mastered it. The 29-year-old programmer consumes logic puzzles at the same rate most of us buy magazines. Behind his desk he keeps an enormous plastic bin filled with dozens of Rubik's Cube-style twisting gewgaws that he periodically scrambles and solves throughout the day. Cohen says he loves Amazons, a cross between chess and the Japanese game Go, because it is pure strategy. Players take turns dropping more and more tokens on a grid, trying to box in their opponent. As I ponder my next move, Cohen studies the board, his jet-black hair hanging in front of his face, and tells me his philosophy of the perfect game."The best strategy games are the ones where you put a piece down and it stays there for the whole game," he explains. "You say, OK, I'm staking out this area. But you can't always figure out if that's going to work for you or against you. You just have to wait and see. You might be right, might be wrong." It's only later, when I look over these words in my notes, that I realize he could just as easily be talking about his life.

Bram Cohen is the creator of BitTorrent, one of the most successful peer-to-peer programs ever. BitTorrent lets users quickly upload and download enormous amounts of data, files that are hundreds or thousands of times bigger than a single MP3. Analysts at CacheLogic, an Internet-traffic analysis firm in Cambridge, England, report that BitTorrent traffic accounts for more than one-third of all data sent across the Internet. Cohen showed his code to the world at a hacker conference in 2002, as a free, open source project aimed at geeks who need a cheap way to swap Linux software online. But the real audience turns out to be TV and movie fanatics. It takes hours to download a ripped episode of Alias or Monk off Kazaa, but BitTorrent can do it in minutes. As a result, more than 20 million people have downloaded the BitTorrent application. If any one of them misses their favorite TV show, no worries. Surely someone has posted it as a "torrent." As for movies, if you can find it at Blockbuster, you can probably find it online somewhere - and use BitTorrent to suck it down.

With so much illegal traffic, it's no surprise that a clampdown has started: In November, the Motion Picture Association of America began suing downloaders of movies, in order to, as the MPAA's antipiracy chief John Malcolm put it, "avoid the fate of the music industry."

For Cohen, it's all a little surreal. He gets up in the morning, helps his wife feed their children, and then sits down at his cord-and-computer-choked desk to watch his PayPal account fill up with donations from grateful BitTorrent users - enough to support his family. Then he goes online to see how many more people have downloaded the program: At this rate, it'll be 40 million by 2006.

"I can't even imagine a crowd that big. I try not to think about it," he admits.

So he does what he always does. He narrows his focus to zoom in on the next thorny problem, the next interesting technical challenge. Like our game of Amazons.

He lays down another piece: "I think I've won now."

Like many geeks in the '90s, Cohen coded for a parade of dotcoms that went bust without a product ever seeing daylight. He decided his next project would be something he wrote for himself in his own way, and gave away free. "You get so tired of having your work die," he says. "I just wanted to make something that people would actually use."

Cohen was always interested in file-sharing. His last job was with MojoNation, a project based in Mountain View, California, that tried to create a "distributed data haven." A MojoNation user who wanted to keep a file safe from prying eyes could break it into chunks, encrypt the pieces, and store them on the millions of computers belonging to people who, theoretically, would be running the software worldwide. Too complicated for easy use, it expired like the other startups Cohen was part of. But it gave him an idea: Breaking a big file into tiny pieces might be a terrific way to swap it online.

The problem with P2P file-sharing networks like Kazaa, he reasoned, is that uploading and downloading do not happen at equal speeds. Broadband providers allow their users to download at superfast rates, but let them upload only very slowly, creating a bottleneck: If two peers try to swap a compressed copy of Meet the Fokkers - say, 700 megs - the recipient will receive at a speedy 1.5 megs a second, but the sender will be uploading at maybe one-tenth of that rate. Thus, one-to-one swapping online is inherently inefficient. It's fine for MP3s but doesn't work for huge files.

Cohen realized that chopping up a file and handing out the pieces to several uploaders would really speed things up. He sketched out a protocol: To download that copy of Meet the Fokkers, a user's computer sniffs around for others online who have pieces of the movie. Then it downloads a chunk from several of them simultaneously. Many hands make light work, so the file arrives dozens of times faster than normal.

Paradoxically, BitTorrent's architecture means that the more popular the file is the faster it downloads - because more people are pitching in. Better yet, it's a virtuous cycle. Users download and share at the same time; as soon as someone receives even a single piece of Fokkers, his computer immediately begins offering it to others. The more files you're willing to share, the faster any individual torrent downloads to your computer. This prevents people from leeching, a classic P2P problem in which too many people download files and refuse to upload, creating a drain on the system. "Give and ye shall receive" became Cohen's motto, which he printed on T-shirts and sold to supporters.