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A new e-mail worm is circulating that has the potential to severely damage machines that it infects, potentially deleting all the files on a computer's hard drive while mocking the machine's owner, according to advisories released by a number of antivirus software makers.

The new worm is called Winevar and was first spotted in South Korea. Its release was possibly intended to coincide with the AntiVirus Asia Researchers conference, which was held in Seoul, South Korea, last week, according to an advisory released by Helsinki-based security company F-Secure.

E-mail messages containing the worm may contain the subject "Re: AVAR (Association of Anti-Virus Asia Researchers," according to F-Secure.

The worm is also known by other names, for example: W32/Winevar.A, W32/Korvar, W32/Winevar@mm, I-Worm.Winevar, and the "Korean Worm."

Variant of Bridex

According to advisories, the worm appears to be a variant of the recent Bridex or "Braid" worm.

Like that worm, Winevar takes advantage of the known IFRAME vulnerability in Microsoft's Internet Explorer Web browser and Microsoft mail clients such as Outlook and Outlook Express. That vulnerability allows attachments in HTML-format e-mail messages to be opened without user interaction.

Also like Bridex, Winevar deposits a variant of the Funlove virus on infected machines once it is run and attempts to shut down processes used by antivirus software. According to an advisory by Moscow-based Kaspersky Labs, there are signs that the worm may also be programmed to conduct a denial of service attack against antivirus software maker Symantec's Web site.

Winevar spreads itself by searching out e-mail files and extracting addresses from them. The worm then uses Simple Mail Transport Protocol to e-mail copies of itself to those addresses, using random series of numbers to disguise the name of the attachment containing the worm, further complicating the task of identifying infected e-mail messages.

Whereas Bridex simply gathered information on the systems it infects, however, Winevar can cause real damage to machines.

Mocking Messages

Once infected machines are rebooted, the worm displays a dialogue titled "Make a fool of oneself" with the message "What a foolish thing you have done!" Clicking on an OK button on the dialogue deletes all files on the computer's hard drive that are not currently opened, according to the security advisories.

Winevar is known to have infected machines, according to Kaspersky Labs.

Most leading antivirus companies have posted updated definitions for the new worm and instructions on removing the worm from infected machines. Users who suspect they are infected are advised not to restart their machine before removing the worm's files.

In addition, Microsoft has issued a patch covering the IFrame vulnerability exploited by Winevar on its Web site, and also has posted a security bulletin about an ActiveX vulnerability used by Winevar.