Dear PropellerHeads: My roommate swears his screensaver searches for aliens. I'm starting to think he's an alien - what is he talking about?!

A: Does he run up huge phone bills calling home every night? Or bogart the Reese's Pieces during movie night? He could be a homesick candyaholic, or...

He's probably running a program on his computer called SETI@home. According to setiathome.berkeley.edu, it's a "scientific experiment that uses Internet-connected computers in the Search for Extraterrestrial Intelligence (SETI)."

The free download runs when your computer is idle - as a screensaver or in the background while you work. It downloads data sets collected from radio telescopes and uses spare CPU cycles to analyze them. The results are sent back to the mothership, so to speak.

The idea is out-of-this-world: by harnessing the resources of thousands of mundane PCs, SETI scientists snag supercomputer-scale strength. What takes years to calculate in a research lab takes only months using your old Pentium III and a few (thousand) of its friends. Far out.

If your idea of little green men is less "space invader" and more "two-inch toy soldier," consider some similar alternatives. From climatologists and mathematicians to chemists and biologists, there's no shortage of lab coats eager to leash your PC's downtime.

The SETI code gave rise to BOINC - the Berkeley Open Infrastructure for Network Computing (boinc.berkeley.edu). SETI is now one of several BOINC projects. A more down-to-earth example is the World Community Grid (worldcommunitygrid.org), currently crunching numbers for Muscular Dystrophy and AIDS research, among other causes.

Stanford University has the similar Folding@home, which studies protein folding and could help find cures for Mad Cow, Parkinson's and other diseases. There's even a version for the PlayStation 3 - see folding.stanford.edu for details. As with BOINC projects, a free account (but no personal information) is required. The really impressive screensaver is worth it.

Technically, these are examples of massively distributed computing using a computer grid. But all you need to know is that while you're asleep dreaming about World of Warcraft and fudgsicles, your computer can stay up late curing cancer and Alzheimer's. Asimov would be proud.

Will this shorten your computer's lifespan? Doubtful. Most people replace their PCs before the hardware dies. Besides, searching for malaria vaccines is more worthwhile than other things your computer could be doing while you're at work, like downloading pirated movies you didn't pay for (tsk, tsk).

Careful, though: A university student was sued a few years ago for installing these programs in a computer lab. No matter how good the cause, you still can't use resources that aren't yours.

But for your own home computer, download one of these important programs today. And if you're still wondering about your roommate, we have an experiment you can try. You'll need a bike with a basket on the front...

When the PropellerHeads at Data Directions aren't busy with their IT projects, they love to answer questions on business or consumer technology. Email them to questions@askthepropellerheads.com or contact us at Data Directions Inc., 8510 Bell Creek Road, Mechanicsville, VA 23116. Visit our website at www.askthepropellerheads.com.