Computer security software firm McAfee Labs issued a warning about a virus spreading through P2P networks disguised as a media file. The Trojan horse looks like either a video or audio file, but in fact is an executable file that serves ads to the affected computer.

The company says it has found the virus on more than 500,000 computers since Friday. The risk is labeled "medium" which in fact is the highest rating given to a potential threat in three years.