Researchers at gateway security specialist Secure Computing have identified a new Trojan virus being distributed in the wild via infected multimedia files.

First detailed in a report posted to the company's TrustedSource research blog, Secure Computing experts said the Trojan specifically infects multimedia files stored on a victim's computer, embedding its content via the ASF (Advanced Systems Format), which is commonly used along with video and audio content in MP3 and WMA music files, WMV video files, and other formats.

When users attempt to play a file that has been infected by the attack, they are prompted to run a fake codec that secretly installs additional malware.

Secure Computing has tabbed the attack as "Trojan.ASF.Hijacker.gen."

"One of the media file infector's capabilities is to also convert MP2 and MP3 files (MPEG-1) into Windows Media Audio (WMA) files. The malware injects a malicious command into any such ASF files on the victim's harddisk, causing Windows Media Player to redirect to a malicious resource on the Web (the fake codec)," Secure researchers said.

When the multimedia file is eventually delivered, and the fake codec is running in the background, the Windows Media Player pop-ups that asked the user to install the initial piece of code disappear in an attempt to convince the user that all is functioning well on the computer -- a tidy way to cut at any potential suspicion that could arise if the user were asked to complete the additional commands.

"Of course, this is just the consequence of the malware simply changing the compromised system's behavior," the researchers pointed out. "By infecting the multimedia files, the attackers promote the spreading of their miscreant through (peer-to-peer) file-sharing networks."

The company warned that users downloading multimedia content from P2P networks need to be particularly careful in light of the threat's design, and to be more attentive to any unexpected pop-ups that appear as they go about their downloads.

Matt Hines has been following the IT industry for over a decade as a reporter and blogger, and has been specifically focused on the security space since 2003, including a previous stint writing for eWEEK and contributing to the Security Watch blog. Hines is currently employed as marketing communications manager at Core Security Technologies, a Boston-based maker of security testing software. The views expressed herein do not necessarily represent the views of Core Security, and neither the company, nor its products and services will be actively discussed in the blog. Please send news, research or tips to SecurityWatchBlog@gmail.com.