You may have succumbed to this fake program: http://www.bleepingcomputer.com/virus-removal/remove-system-defragmenter or something very similar.
Follow the removal instruction therein. They will work for most of these fake panic attacks.
It isn't a virus but it's a darned nuisance.
Message was edited by: Ex_Brit on 05/01/11 6:18:36 EST PM