Are you using AVG free? has it been good protection so far? I am currently no longer installing AVG free on user's computers who do not have paid antivirus protection. I am now installing Microsoft's own antivirus protection called "Security Essentials".
If you have recently come accross a program called "Security Tool" that is running on your computer, and claims to have found viruses, unfortunately you do have viruses - and "security tool" is the culprit.