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Klez-H tops virus charts – again

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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 524, 507 copies of the virus in May, compared to 422,507 in April.

MessageLabs reports that virus infection rates are currently running at around one per 200 emails, which compares to one in 30 infected emails at the heights of the Goner and Love Bug epidemics.

In the last four weeks MessageLabs blocked more than 650,000 emails infected with various variants of Klez, which became the worse virus ever this month, according to the company.

By comparison, the next most common virus, SirCam, was blocked only 21,124 times by MessageLabs during the last four weeks.

A chart of calls logged by AV vendor Sophos reveals much the same picture with Klez responsible for more than half the calls to the company in May. The next most common pathogen was ElKern-C.

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 May


  1. Klez-H
  2. Klez-E
  3. SirCam
  4. Magistr-B
  5. Hydris-B
  6. Magistr-A
  7. BadTrans-B
  8. Yaha-C
  9. Fortnight
  10. Gibe-A

    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
    Klez worm infects and infuriates
    Cisco and Sophos spoofed in virus mail-outs
    SirCam virus hogs connections with spam
    Virus writers outpace traditional AV

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