For those of you that have out of date computers, please read this.
There are a number of anti-virus software scams out there, such as Internet Antivirus Pro, which are actually viruses themselves. They come from websites that are deliberately or unintentionally coded to show a message such as "Warning! Your computer is infected with viruses, a free scan will reveal these as well as other malware." with two choices, either that you click on will show a graphic with several drives (local disk C, local disk D, floppy disk A, and CD drive E) and it will say that they have viruses. Check the website you are on (it is usually something with .co.cc at the end) then close out of the window. It will show something else as well as a download (CLOSE OUT OF IT) and will close out, the link will die, and your computer won't be infected.
If you have downloaded it, and installed it, you need a free program to uninstall it (if you haven't already paid the fee(around a hundred dollars)) and your computer will be clean.
There is a video on youtube, Here watching it as it happens.