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.
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
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