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The W32.Klez worm and its variants are still loose in the wild more than a week after the latest variant was discovered, moving antivirus software vendor Symantec to upgrade it to a level 4 virus threat on its danger scale of five.

Symantec says it is receiving more than 3,000 submissions a day of W32.Klez and its variants. At the peak of the SirCam virus, in mid-2001, the company received about 1,500 daily submissions, Symantec of Cupertino, California, says in a statement.

"The number of submissions warrants a level-four rating," says Andre Post, senior researcher at Symantec. "But you have to see this in perspective. The submissions are for all W32.Klez variants--W32.Klez.E and W32.Klez.H are the main two contributors to these numbers."

W32.Klez.H, the latest variant of the W32.Klez mass mailer worm that first surfaced last year, was discovered on April 17. A variant of a worm contains attributes of the original, but has been altered so that it behaves differently. Updated virus signatures from leading antivirus software vendors should protect against the worm.

Hitting Home

Home users, not corporations, are being hit by W32.Klez, according to Post.

"Based on analysis of Thursday's submissions I can say that 5 percent or less of all the submissions that we get are from corporate users. The overwhelming majority is from home users. Corporations have learned that they need to protect themselves from worms and viruses like these," he says.

Marius van Oers, a virus research engineer with Network Associates in Amsterdam, says W32.Klez is spreading worldwide and is "one of the biggest virus threats today, but not historically."

It's not a one-day phenomenon, he says. "It started slowly and we have seen the spread accelerate in the last week."

Network Associates rates the worm "medium" risk, but that really only goes for home users, according to Van Oers, who agreed that W32.Klez finds most of its victims among home users.

"We aren't worried too much about the corporate users as they work with updated virus definitions and filtering on file extensions. However, we are seeing reports from home users. The risk level for corporate users is slightly below medium, but it is certainly at medium for the home users," he says.

Updated Protection

Both Symantec and Network Associates advise users to check if they have recent virus definition files installed. Symantec offers a special software tool to remove the virus.

W32.Klez.H arrives in an e-mail with a random subject line and message body. The sender's e-mail address can be spoofed. Once launched, the worm sends itself to all addresses it finds in the Windows address book, the database of instant-messaging program ICQ, and local files. A file from the user's system is randomly selected and sent along with the worm.

W32.Klez.H also attempts to disable antivirus software and drops another virus in the user's system that tries to infect executable files there and across network filing systems, according to antivirus vendor write-ups of the worm.