Virus writers seem to have taken Christmas off, with fewer viruses emerging in January compared to December.

Antivirus firm Sophos reported no change in its virus top 10, which ranks Zafi-D in the top spot for the second month running.

The company recorded a slight reduction in the number of new viruses: during December 4.3 per cent of emails contained some form of virus compared to 5.6 per cent the previous month.

"Zafi-D tops the chart for the second consecutive month, accounting for nearly half of all reports in January," said Graham Cluley, senior technology consultant at Sophos.

"It's disturbing that this worm, which spreads under the guise of a Christmas greeting, is continuing to cause so much trouble into the new year. Recipients are probably opening these mails thinking they have received belated Christmas cheer from a friend or colleague."

Things have been busier on Sophos' internet hoax list. The number one hoax, for the seventh month in succession and accounting for 31 per cent of this type of email, is the Hotmail hoax. This claims to be a warning from Hotmail about shutting down users' accounts.

The tsunami in south east Asia was found to have spawned two new entries. One has a picture of an unnamed survivor asking for details on who he is, although he has already been identified as Swede Hannes Bergstroem.

The other is a variation on the 419 Nigerian letter fraud, claiming to come from a Thai man looking to deposit $3.8m in a European bank account.

The top 10 viruses and hoaxes reported to Sophos in January 2005 can be seen here.