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Symantec discovered the worm on 29 December. Also known by its subject line, "ZaCker," the worm deletes system files and antivirus files that have not been updated to detect it.
The worm spreads by mailing itself to users through Microsoft's Outlook e-mail program, according to Symantec.
The worm is attached to messages with the subject lines: "If you have an elegant taste" and "For everybody wants to marry a woman that he doesn't love!" Symantec said. Once activated, the worm deletes various files with suffixes including .INI, .EXE and .JPG.
Symantec has rated the damage potential of the virus as medium, while rival antivirus vendor McAfee has rated it as low risk.
"We have not seen enough to upgrade it to medium risk," said April Goostree, virus research manager for McAfee.
With several worms that attack antivirus software emerging in recent months, McAfee recommends customers use a firewall in combination with antivirus software, Goostree said.
Goostree suggested that another way to prevent the spread of the worm would be for customers to stop using Outlook. "It's using Outlook and [Outlook] Express to propagate," she said. "It doesn't have the ability to send itself."
However, although using other e-mail applications would not spread the worm to others, few see straying from Microsoft as an option.
Symantec Security Response: securityresponse.symantec.com