Klez variant crowned virus king

A variant of the Klez virus has taken the crown as the biggest virus of all time, usurping last year's SirCam outbreak and even the infamous Melissa and I Love You viruses.

Statistics from antivirus firm MessageLabs found that the Klez.H variant overtook SirCam on Sunday, clocking up 775,000 copies.

Around 20,000 instances of Klez.H are now being logged on average everyday, working out at one infection every 300 emails.

SirCam surprised security watchers last summer by storming inboxes everywhere and maintaining a rate of growth even bigger than the Melissa epidemic.

The reasons for Klez.H's success have been put down to an ability to cover its tracks by using a random name from an infected machine's address book as the sender address, as well as using a large selection of subject lines.

Alex Shipp, a virus researcher at MessageLabs, explained that when SirCam broke out last summer, experts believed it to be one of a kind. But the rise of Klez.H signifies that SirCam was not a one off, but the start of a trend.

"Klez.H has shown us that highly sustainable viruses will continue to appear. It is easy to become blasé about new viruses as most people are now far more aware of the dangers," he said.

"It represents a new trend in virus writing to continually modify viruses until they foil enough antivirus scanners to spread successfully to email users worldwide."