hate to say, but sounds like a virus, unplug your connection to internet, click start - run (type %temp%) -ok, select all - delete. this should delete all your temperary files, go to recycle bin and empty, next run all your virus scans, go to internet options in control panel, delete cookies, history etc + offline content, if using the new explorer, delete each option seperately as well as the last all option. Restart your computer (offline) again check your temp folder( run -%temp%) this folder should be empty . if so you will be ok to start back online, then update all your anti virus, anti spyware programs etc also, update windows.
Hope this helps, had same problem once, now I have taught the family how to keep computers clean at all times, most people think that by deleting using the given tools that this alone clears unwanted stuff from your computer, however, most nasty stuff hides itself in this folder, this folder should ideally be kept clean, i would not be surprised if you have a few files in this folder, some files may not delete, this is sometimes because they are being used by yourself, eg msn messenger, any files that you can't delete as previously explained then contact me and I will explain how to get rid of them.