Klez tops virus charts – again

No sign of let-up

Variants of the Klez worm were by far the most common viruses circulating on the Internet this month. Again.

That's according to monthly statistics from managed services firm MessageLabs, which stopped 788,137 copies of the virus in June, compared to 524, 507 in May.

Virus infection rates are currently running at around one per 240 emails, which compares to one in 30 infected emails at the heights of the Goner and Love Bug epidemics, MessageLabs reports.

Klez became the worst virus ever in May, and it shows no sign of abating, according to the firm

Other viruses were much less common. The next most common virus, Yaha, was blocked only 67,146 times by MessageLabs during the last four weeks. However Yaha has become a major irritant at Vulture Central because of its capacity to spew hundreds of infectious emails to a single address from infected machines.

Very irritating.

Klez cleanup

Klez is a mass-mailing worm which searches the Windows address book for email addresses and sends messages to all recipients that it finds. The worm uses its own SMTP engine to send the messages. It can also spoof the 'From' in messages, a factor which has resulted in widespread confusion about the bug.

The subject and attachment name of incoming emails is randomly chosen, making it harder for users to spot. The attachment will have one of the following extensions: .bat, .exe, .pif or .scr. Klez is capable of infecting files.

The worm exploits a vulnerability in Microsoft Outlook and Outlook Express in an attempt to execute itself when you open or even preview the message. Information and a patch for the vulnerability can be found here. ®

Top ten viruses blocked by MessageLabs in June


  1. Klez-H
  2. Klez-E
  3. Yaha-E
  4. SirCam
  5. VBSWG.AQ
  6. Magistr-B
  7. Hybris-B
  8. Magistr-A
  9. Yaha-C
  10. Frethem-F

    External Links

    Analysis of the spread of the Klez-H worm by MessageLabs

    Related Stories

    Klez-H is the worst virus ever - official
    Klez storms monthly virus charts
    Virus writers outpace traditional AV

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