Read more here: Netcraft — Phishing Attacks Using Banner Ads to Spread Malware

You _might_ be smokin’ crack. I don’t know how SETI loads up data on each of the client computers, but I think you’d run into a bunch of implementation problems, the least of which being your computing environment is a web browser plugin, which isn’t designed to do heavy mathematical computation.

Within the span of time a user is on a page (1 min, as you say) you have to 1. transmit work data 2. do the work 3. send the results back. I’m willing to bet 1 and 3 are not trivial tasks.

Also, you’d have to give this task a low thread priority, or you’d hijack the browser. I don’t even know if you can ask for that within the confines of Flash.

The devil, as they say, is in the details. But still, a cool idea.