Spyware! Unlike viruses, which are simply malicious pieces of code that you don't want, spyware is usually attached to programs that you do want. It's kind of like porky riders on legislative bills - a nifty law you want passed has attached to it a proviso to raise taxes a billion percent, that sort of thing. When you install the program you want spyware may get installed as well without your knowledge or permission - nasty. Spyware usually serves to collect info about you and sent it back to someone and/or to bring you ads. In fact, ad-sponsored programs are using spyware but since they admit they're ad-sponsored up front it's not truly spyware.

Anyway. Three very bad cases at that but relatively easy to cure. I used two programs to get the computers happy again. The first is Ad-aware. Get the free version now! It sniffs out spyware and gives you the means to remove the crap. It is possible that the programs which brought in the spyware may need it to run, removing the spyware component may kill the parent program. Well, find a different program - one that doesn't include spyware. There's plenty of alternatives.

The other program is System Mechanic. It's shareware and I recommend it for it's variety of tools. For spyware though the tool you want is one that let's you edit the startup programs listed in the Registry. System Mechanic will let you disable the entries and for most of them you will. Which ones I can't exactly tell you but compare what you see on an infected machine to one non-infected and that will give you a good clue as to which programs are unneeded.

The idea is to wipe out the spyware programs and to wipe out the startup calls. Also, check under Start | Programs | Startup and see what's there. You likely won't need whatever entry you find. In fact for a nice happy computer you shouldn't have a bazillion programs, like your IM, winamp, real, your video tweaker, etc. automatically load on bootup. For Windows lean + clean = happy pc.

Caveat: Advice here doesn't apply to Linux users. Not yet.