Adware and spyware is not necessarily classracer's fault. A user can inadvertently allow adware access to your browser through many sources. This link is a good description of steps you can take to remove adware from your computer if you are using Internet Explorer:
http://antivirus.about.com/od/spywar...arespyware.htm
If you are using firefox, Chrome or a MAC, you are on your own.