Something going on with your system files.  I would think that it's from a virus, but I don't want to assume.  Run your virus protection software and see if this identifies a virus.  If so, remove virus and retry.  If not, repair your OS install

It could also be spyware. Best thing to do is a full system scan for virus' and spy ware. You could also try the IE repair feature or download a fresh copy of IE from Microsoft and write over your existing IE and hope that works, else possible OS reinstall will take care of it.

Joe L