Maybe spyware gone awry. Try "spybot search and destroy" and adaware. Do
NOT use any of the imitations (which are themselves, spyware).
www.safer-networking.org and
www.lavasoft.com.
But moreover (and I'm sorry to sound mean) that should teach you a lesson about Microsoft Internet Explorer. As an IT professional who deals with security vulnerabilities all of the time, I can say that IE is the swiss cheese of security (full of holes). I recommend Firefox personally there are
very few sites now days that don't work on Firefox, plus you eliminate 99.99% of the potential problems with spyware (it's hard to get spyware to stick on Firefox).