A new piece of malware is on the loose, principally infecting computers using Peer-to-Peer software like Limewire and Edonkey.

The malware looks like an ordinary media download, but when the user tries to play it , they are prompted to install a codec to play the file.

If they comply, the computer is compromised and they are plagued by endless pop-ups.

Over 500,000 computers have been reported infected in the past week.