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The worm is not destructive and has not yet infected many systems, but as with any mass-mailer worm, could become a nuisance as unsuspecting users spread it. Like other mass-mailing worms such as the Anna Kournikova worm or Badtrans, Gokar spreads through Microsofts's Outlook and Outlook Express e-mail clients. It activates when a user clicks on an attachment sent with the infected message, according to antivirus firms Symantec, F-Secure, and Trend Micro. Infected e-mail arrives in user inboxes with dozens of combinations of different subject lines, body messages, and filenames, though each attachment will end with the .PIF, .SCR, .EXE., .COM or .BAT extensions, the companies said.

When the attachment is double-clicked, the worm installs a file called Karen.exe on the infected system and mails itself to all addresses listed in the computer's address book. The worm then runs every time the infected computer is booted up. Whether a system is infected or not can be determined by searching for the Karen.exe file.

Other Targets

The worm also uses the chat program Internet Relay Chat (mIRC), the companies said. Gokar searches the infected PC for the mIRC application, and if it finds it, attempts to infect IRC users in the same discussion, or channel, as the infected system whenever the application is started, according to Trend Micro.

Lastly, if an infected system is running Microsoft's Internet Information Services Web server software, the worm will modify the default Web page on the system and offer users visiting the site a chance to download the worm, according to F-Secure. An infected Web site will be changed to display the text "We are Forever" and point users to a link to download a file called Web.exe, which contains the Gokar worm, according to Symantec.

The Nimda worm also defaced Web sites and downloaded files to the computers of users viewing the site. Unlike Nimda, which automatically downloaded a file through the browser, Gokar requires that the user click a link to download the worm. Both Nimda and Code Red exploited IIS to assist in their spread.

Users should check with their antivirus companies for software updates. Companies are urged to block attachments, especially .exe., .scr., and .pif files, at their mail gateways to avoid infection.

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