Email viruses are now almost twice as prevalent as they were in 2001, with one email in every 200 containing a virus.
Virus-scanning firm MessageLabs said it stopped 9.3 million viruses in two billion emails this year, which equated to one virus in every 215 emails. This is compared to 1.8 million viruses stopped in 718 million emails in 2001, or one virus in every 398 emails.
According to the report, which measured results up to the end of the second week of December, the most active virus was Klez.H with 4.9 million copies stopped by MessageLabs. Yaha.E came second with 1.1 million copies, then it was Bugbear.A with 842,333, Klez.E with 380,937 and SirCam.A with 309,832. These figures only represent the numbers stopped by MessageLabs for its corporate customers. The actual numbers of these viruses are much higher.
Although Klez was the most active virus, Bugbear was the most dramatic outbreak of the year, infecting one in every 87 emails at its height in October. Its dual-mode attack saw it accounting for 30 percent of all reports of viruses to antivirus Sophos in the last month -- well ahead of former top spot incumbent Klez, which by then only accounted for around 8 percent of all reports in third place.
Klez could only reach one in every 169 even at its peak, while Yaha never rose above one every 268, said MessageLabs. The two most dramatic outbreaks of all time recorded by MessageLabs remain Goner, at one in 30 last December, and the number one LoveBug, which hit one in every 28 in May 2000.
Alex Shipp, senior antivirus technologist at MessageLabs, said the more prevalent viruses owed their success to the fact that people found them hard to spot. "This is because these are able to 'spoof' email addresses, so that the identity of the real sender is difficult to trace," said Shipp. "It also means that by mass mailing contacts from a recipient's address book, further victims are likely to open the rogue email, because they think it is from someone they know and trust."
Shipp put the blame for the preponderance of emails on home users, who tend to have the least protection.
Security companies are expecting a further rise in the number of email viruses over the Christmas period. Antivirus vendor Sybari last week warned network administrators of holiday offers and greetings that may also be carrying more than holiday cheer. Joe Licari, director of product management at Sybari, said: "During the holiday season, employees need to pay close attention to the email they get in their inbox."