The W32.Klez worm and its variants are still loose in the wild over a week after the latest variant was discovered, moving antivirus software vendor Symantec Corp. to upgrade it to a "level 4 virus threat" on its danger scale of five.
Symantec said it is receiving over 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, said in a statement Thursday.
W32.Klez.H, the latest variant of the W32.Klez mass mailer worm that first surfaced last year, was discovered on April 17. Updated virus signatures from leading antivirus software vendors should protect against the worm.
Marius van Oers, a virus research engineer with Network Associates Inc. in Amsterdam, said 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 said. "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.
"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 said.
Both Symantec and Network Associates advise users to check if they have recent virus definition files installed.
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.