Did you already have an anti virus on the computer ? There is one out that that acts like a virus to scare you into downloading it . pops up with multiple windows and scans showing all different "bad" things on your computer . Wish i could think of the name , because I bet it is in your software add/remove list and if you removed it you would be ok. have you scanned the add/remove software list and looked for a program that was just ran on the day that this happened ?