New worm transcodes MP3s

A new kind of malicious software could pose a danger to Windows users who download music files on peer-to-peer networks.

The new malware inserts links to dangerous Web pages within ASF (Advanced Systems Format) media files.

"The possibility of this has been known for a little while, but this is the first time we've seen it done," said David Emm, senior technology consultant for security vendor Kaspersky Lab.

Advanced Systems Format is a Microsoft-defined container format for audio and video streams that can also hold arbitrary content such as images or links to Web resources.

If a user plays an infected music file, it will launch Internet Explorer and load a malicious Web page that asks the user to download a codec, a well-known trick to get someone to download malware.

InfoWorld Article

Pay attention to file size. If MP3 file size is, for example 64Kb, it's not any full lenght song. Typically MP3's are about 5Mb's.

What is comes to ASF files, they are (usually) streaming files. P2P programs usually contains filetype filters, so good thing to do, is add ASF to that list.