SETI@home aims to tackle one of the biggest computing problems in history, so big that a $900 home computer may wind up solving it--if a $100 cell phone doesn't get there first.

The Search for Extraterrestrial Intelligence at Home is the highest-profile experiment yet in "distributed computing." This approach breaks gargantuan problems into smaller segments that can be attacked with personal computers, then uses the Internet to send out these slices and collect the results. It's a rough equivalent of Tom Sawyer getting every other boy in town to whitewash the fence, one plank at a time.

So far, more than 1.4 million people in 224 countries have downloaded the SETI@home software and used it to sift through the 35 gigabytes of raw data that the Arecibo Observatory radio telescope in Puerto Rico collects daily. This free program, available for Windows, Mac and Unix systems, downloads a 350-kilobyte slice of the information recorded by Arecibo's 1,000-foot-wide dish. Then, whenever the computer is idle, the program analyzes this data--a "work unit"--for unusual signal patterns, displaying the results as a "Star Trek"-ish screen saver. When finished, the program sends the information back to the SETI servers and downloads more data.

Sifting through the billions and billions of bits of data that Arecibo collects is a monumental task, but on the other hand there's the chance, however slight, that your rusty old PC might be the one that first detects a signal. "The search for extraterrestrial intelligence is the biggest question that faces us, outside of how the universe began," said David P. Anderson, project director of SETI@home and a former professor at the University of California at Berkeley. "[It's] something that attracts a lot of people."

That altruistic pursuit, however, isn't the only reason people are flocking to SETI@home. The site has also attracted what Anderson calls "computer hot-rod guys," who compete to see whose machines can process information the fastest. SETI@home keeps statistics on individual users and groups of users, and the results are posted in a top-1,000 list. It's a subculture all its own, and SETI@home isn't the only site where this online "sport" is being played.

On Distributed.net , more than 60,000 computers are working together to win a code-breaking contest sponsored by RSA Data Security. The Bedford, Mass.-based firm, in an effort to prove the ineffectiveness of current, government-sanctioned encryption methods, is offering $10,000 to the first group that cracks a "64-bit" key (the number indicates the complexity of the equation behind that key). Like SETI@home, Distributed.net keeps track of how much data different teams of users are processing and ranks them accordingly. As the competition heats up, different groups with different allegiances vie for the top ranking.

"People were joining together and forming teams even before we formalized the process on our server," said David McNett, president and co-founder of Distributed.net. "We have teams I never would have guessed would have an organized interest in our project: school teams, company teams, bird-watcher teams . . . anything you can imagine."

Colin Hildinger, for instance, runs Team Warped, made up of people who use and support the IBM OS/2 operating system. For dedicated computer aficionados, the choice of an operating system is a very personal expression of who they are--hence the attempts to display its prowess. At Distributed.net, even the long-forgotten Amiga platform has a team competing for the prize.

"We know that the odds of our team winning aren't that great," Hildinger wrote in an e-mail. "Currently the odds are about one in 100 that Team Warped will find the key, and the odds that it will actually be an OS/2 machine are much worse. But every OS/2 user involved would love to have the name OS/2 somehow associated with winning one of these contests."

In the meantime, one of Hildinger's main concerns is that his team stay ahead of Team Win32, the Windows group. Nobody, it seems, wants to see Microsoft win--online or in the courts.

But none of these teams is likely to crack this problem any time soon, as only 15 percent of the possible solutions have been checked since the contest began Oct. 22, 1997. Hildinger noted that this could be a problem: "When the current project looks like it will drag on for years and future projects are vaporware, it's hard to get motivated to do anything."

The site does have other computing projects on the horizon, however, including a variety of cryptological and mathematical problems. More interesting, but less likely, is the possibility that the rendered animation for the next "Toy Story" movie could be done over the Internet. McNett said the big obstacle there isn't technology, but copyright-protection issues.

As for the SETI@home project, Anderson predicted it would be completed within two years, assuming no signals from extraterrestrials are found before then. After that, the group plans to start analyzing recordings from a telescope in Australia, covering radio sources in the Southern Hemisphere sky. And faster DSL and cable-modem connections could make many other projects possible.

"There may be approaches to finding a cure for cancer that are computational," Anderson said. "We could use computers to simulate the way that drugs might work. Another possible project involves the simulation the ecology of the planet, predicting global warming. A lot of areas of science are starting to replace laboratories with computers."

And it need not just be traditional computers doing the work. Already, Anderson has been in contact with someone interested in running SETI@home on his Nokia cellular phone. He said, "They're going to be putting computers into everything, so you might someday have your toaster oven doing scientific projects while it isn't in use."