I have just had another person show me a computer with XP Antivirus 2012 on it. This is a virus/malware, not antivirus. It takes over your computer, preventing you from doing anything, including running removal software. It is sneaky, and usually gets on computers when you download "required codec or add-on" for viewing a video or doing something on a web site.
There are a variety of variants of this virus and it changes names depending on the operating system and year. There is a version for XP and Vista. There
The virus keeps showing you security alerts and fake virus on your computer to try to get you to purchase "the full version" of the product. It's a scam.
Below is a link to instructions on how to remove it.
Make sure you always keep your anti-virus and malware protection up to date.
And remember, Apple products are not immune from malware, virus, and hacks. So protect your system.
5 Free utilities for Windows - very useful and powerful (includes AVG Free)
Ad-Aware free download