I see this one come in a lot at work. There's an "antivirus" program called either XP Antivirus 2008 or Vista Antivirus 2008 that claims you have x number of infections and to buy this program to remove it. I'm sure some of you have gotten this, I did. If you leave it on there too long it may be too late to remove, but there's a program called Malwarebytes' Anti-malware that is very good at removing this infection. Just google "malware bytes".
good luck
Malwarebytes, got rid of it no problem.