Unless a flash ad in one of your open browser tabs has gone rogue, it’s likely you’ve got a few spare processor cycles available on the PC you’re using to read this.

And if someone were to appropriate just a few of them – too few for you to notice – then you and all the millions of other web surfers out there could be harnessed together like some kind of gigantic insectoid computing hive mind.

The result would be one of the world’s most powerful supercomputers.

That’s the dream, anyway, of a project called MapRejuice. It’s MapReduce - the algorithm invented at Google that powers more or less all the massively parallel processing on which the web’s biggest businesses rely - but implemented in javascript. And it runs in the background of any webpage on which it’s installed.

You could be running it right now without even knowing it.

Using the spare cycles of the world’s internet-connected PCs is nothing new - SETI@Home has been doing just that in service of parsing radio signals from outer space since the late 90’s. There are also dozens of projects that use the BOINC system on which SETI@Home runs, in order to serve scientists who need cheap access to supercomputer-scale computing power to work on problems ranging from cryptography to protein folding.

But MapRejuice doesn’t require special client software, which means pitching in on giant computational problems could be as simple as leaving the appropriate browser window open.

Right now MapRejuice, which remains primarily a proof of concept, isn’t doing that much. The graph on its homepage reveals, in real time, that it’s doing about 300 jobs per minute right now.

Its ultimate capacity? Well, how many spare cycles do all the world’s internet browsers have?

If you’ve got a site that serves users who wouldn’t mind contributing a little processing power to the project, you can grab the line of code you’ll need to drop into your site’s HTML here. Or, if you’ve got a gigantic problem in need of a MapReduce cluster of nontrivial scale, sign up your project here. And if you just think it’s a cool idea, you can vote for it (it’s an entry in the node.js contest) here.