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.
When you bought your Windows Computer or Laptop did you find it came with a load of pre-installed programs on it? You might have instantly been interested to see all these new programs, and explored some of them. However each one installed can slow your computer down, making booting up your computer and loading up programs you want to use much slower.