HOW TO REMOVE FAKE SOFTWARE, TROJANS AND VIRUSES:
Download, update and scan your computer with Malwarebytes and SuperantiSpyware, delete what ever they find, if this fails to completely remove the infection download then update Avast and run a boot scan (click schedule boot-time scan and restart your PC), all the software below is completely free and safe to use.
If your infection is proving hard to remove run SmitfraudFix following the guide below.
Malwarebytes: http://www.malwarebytes.org/mbam.php
SuperantiSpyware: http://www.superantispyware.com/
Avast Anti-Virus: http://www.avast.com/eng/avast_4_home.html
SmitfraudFix: http://siri.geekstogo.com/SmitfraudFix.exe
Guide to using SmitfraudFix: http://www.bleepingcomputer.com/forums/topic17258.html
To protect your PC in the future you need to use anti-virus software and a firewall, id recommend using Avast and Comodo Pro firewall both are very effective and completely free, you should also switch to Firefox 3 if you are browsing with IE as its much safer. (links on my profile)