Viruses can be nasty and hard to get rid of. They can cause your computer to slow down, install keyloggers resulting in identity theft, even prevent you from starting your PC. I recommend having Avira or AVG free edition installed, along with a router and a software firewall. However, even with the proper protection, viruses can get through and be tough to eradicate. Sometimes, the only solution is to backup your important files, wipe out your machine and start from scratch. But before we get to that point, give me a chance to rid you of that nasty stuff!