Lirva (w32.Lirva@mm), also known as Naith, is a mass-mailing worm that is UPX-compressed to a file size of 32,766 and arrives via e-mail either announcing a new Microsoft patch or offering fan access to Avril Lavigne. Once active, Lirva will attempt to e-mail copies of itself to all contacts on an infected system, shut down all antivirus and firewall programs, and launch a Web browser to open the Avril Lavigne Web site on an infected user's desktop.

Lirva uses the Iframe vulnerability, so on unpatched systems, the worm will automatically execute whether or not the attached file is opened. Antivirus vendor MessageLabs reports that parts of the Lirva worm code very look familiar, so Lirva may turn out to be a variant of a known virus family. Because this worm sends e-mail but is not considered destructive, it rates a 4 on the ZDNet Virus Meter.

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