Klez has claimed a remarkable 13th month in the top 10 list of most frequently occurring viruses - raising concerns about the vigilance of IT managers and administrators charged with updating their company's antivirus software.
The unshakeable malware was the most common virus in February, accounting for 13.7 percent of all reported instances of viruses, according to statistics compiled by Sophos.
Second on the list was relative newcomer Sobig with 7.7 percent.
There was a new entry for Lovgate (also known as Lovegate), which arrived late in the month but managed to claim ninth place with 2.1 percent of reports. The rest of the list comprised the 'usual suspects' - viruses which have been dogging mail servers and administrators for months, such as Yaha, Bugbear and various variants of some of the big hitters of the malware world.
While most updates to antivirus software should safeguard against infection from these viruses, administrators are advised to double check their protection. The fact that Klez is still so prolific after 13 months suggests its longevity is, in part, down to a lack of appropriate updates being applied.
Comparing Klez to newcomer Lovgate, Graham Cluley, senior technology consultant at Sophos, said: "The Lovgate worm may have been the most talked about virus in February, but it certainly wasn't the most prolific, reaching only number nine in the chart. A worm with altogether more substance is this month's number one -- Klez.
"Klez, in its various guises, has now been hanging around the chart for thirteen months, making it the most persistent worm ever. People infected by Klez couldn't have updated their protection in yonks."
Sophos detected 541 new viruses, worms and Trojan horses in February.
