Here's a first: a Trojan horse that actually helps security pros do their jobs.

Analysts at SophosLabs, the research arm of antivirus software vendor Sophos, have discovered a spyware-borne Trojan, dubbed Troj/Erazer-A, that seeks out and destroys movie and music files that it suspects to be illegal copies transmitted via peer-to-peer (P2P) file sharing networks.

The Trojan looks through P2P file sharing folders, seeking out formats such as AVI, MP3, MPEG, WMV, GIF, and ZIP. When it finds these files, it wipes them out and places a copy of itself in the folder, using tempting names such as game.exe, goporn.exe, nero7.exe, and officexpcrack.exe, according to Sophos.

Researchers say that, while some IT departments may be tempted to keep a Trojan that deletes files enterprise users aren't supposed to have anyway, they should think twice.

"The Erazer Trojan is a vigilante worthy of a Charles Bronson movie, taking the law into its own hands. However, it's perfectly possible for the Trojan to aim poorly and wipe out innocent files, too," says Graham Cluley, senior technology consultant at Sophos. "Malware is not the way to fight Internet piracy."

Trojan Erazer could be dangerous because it tries to turn off antivirus applications and other security tools, the researchers observed, noting that its methods are worrisome because it deletes files, steals information, adds itself to the registry, and then drops more malware on the target system.

Still, other security monitoring groups consider the risk to be negligible. The French Security Incident Response Team (FrSIRT) ranked Trojan as "low risk," its lowest incident rating.

P2P, by contrast, continues to be a growing threat to enterprise security. Reconnex, a risk management company, reported that it found P2P protocols in 78 percent of enterprises during the first quarter of 2006, compared with 35 percent in all of 2005. (See Reconnex Targets Threats.)

Trojan/Erazer can be removed with most Windows anti-virus tools, using the same practices used for any other virus, experts said.

— Tim Wilson, Site Editor, Dark Reading

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