Install and use antivirus program. Also install anti adware/spyware program.
Lavasoft's AdAware does pretty good job and it
is free. You can get it at www.lavasoftusa.com -> download...
Since it works like Antivirus program it needs to be updated to get latest
signatures.
Also delete all the Cookies on your PC and all the Temporary Internet Files.
Also to protect your PC, install and use Antivirus. Don't forget to update
it at least once a week. And to keep your PC healthy, update it regularly.
Visit www.windowsupdate.com