The odds are pretty good that this will never happen to you, but should a floating head of U.S. President Barack Obama pop up on your desktop Monday morning, know this: You've been hit with the Obama worm.

The worm was spotted this past Monday after it infected PCs at a preparatory school in Metairie, Louisiana, and was first reported by Walling Data, a value-added reseller in Claremont, North Carolina. Though it is not detected by any antivirus products right now, it is not considered to be a serious threat because it has infected so few systems.

The worm spreads via USB drive, using the Windows autorun feature to install itself automatically on any drive it connects with. Unlike most of today's profit-driven malware, the Obama worm doesn't steal your credit card number or turn your PC into a remote-controlled zombie system. In fact, it isn't designed to do anything besides float a small picture of Obama at the bottom right corner of your desktop all day every Monday.

Unfortunately, it is so badly written that the worm gradually renders any PC it is run on completely useless, according to Rob Koliha, Walling Data's director of innovation. "It will basically prevent execution of any kind of files."

Because antivirus programs don't detect it yet, it's also hard to know when you've been infected, except on Monday.