The roundup of antivirus infections for November has shown a busy month for MiMail variants, but Klez H is still hanging in the top 10 after almost two years.

There is the usual dispute over which virus is most common, but the Sober and Swen worms have scored highly.

"Sober has had a big impact because it's in English and German and many Germans don't expect viruses in their own language," said Graham Cluley, senior technology consultant at Sophos.

"We're also seeing new MiMail viruses cropping up and there seems to be organised intent behind it; the authors have targeted users and anti-spam websites. Definitely one to watch."

So far 12 MiMail variants have been found, ranging from simple email harvesters to 'phishing' attacks that seek users' PayPal or bank details. The worm is thought to have originated in Eastern Europe.

Klez H is still in most charts, making it one of the most persistent viruses in history.