Email spammers are using MP3 attachments to bypass the anti-spam filters. Spammers are taking advantage of the fact that the MP3 format is one of the most common in use today and that most anti-spam solutions do not handle attachments very well because they do not actually analyze the attachment content.

It’s a short, 30-second MP3 file recorded at low bit-rate with a synthetic female voice promoting a particular stock; the voice heavily distorted to avoid signature-based anti-spam approaches.

To address the MP3 spam threat administrators need to deploy as many anti-spam techniques as possible, including Bayesian filtering, while at the same time maintaining a very low level of false positives. Additionally, administrators can block attachments or place restrictions on allowable sizes to weed out unwanted material.