Spyware removal programs such as Adaware and Spybot Search and Destroy do a pretty good job if you run them from time to time.
My brother's girlfriend has a daughter that is constantly downloading all kinds of junk off of the Internet. My brother cautioned her that she was garbaging the computer with all kinds of Spyware and viruses, but she didn't seem to care one way or the other. Teenagers can be like that.
Finally, she had gathered so much stuff on it that my brother asked me to go over and try to fix it. When I arrived, there was so much junk on it that pop ups and other malicious wares kept jumping in front of me that I couldn't even make a boot disk so I could delete the partition to start again.
We wandered next door to one of her neighbor's house. The neighbor allowed me to use his computer to make a boot disk. There was spyware on his computer, though not nearly as bad. I installed a copy of Adaware on his PC and wiped most of it out. Then I was able to make a boot disk and also downloaded onto the boot disk a piece of freeware called 'Delpart' that will wipe out any partition you care to blow away ('be careful how you use it', to steal a slogan from an old Hai Karate commercial).
When I returned to the computer the teenage girl had trashed, I rebooted on the floppy and used Delpart to blow away her partition. The I created a clean one and reinstalled the OS.
Of course, the teenage daughter lost all of her files. But she had been cautioned that that would happen at the rate she was going. I installed Adaware and Spybot Search and Destroy and showed my brother's girlfriend how to run them.
It can be a real mess.