The warning came from Mark Price, technical director of anti-virus firm Panda Software. "There will be no change in the number of viruses, but we will get seasonally related ones. There have been a lot of virus variants and we expect to see new variants over Christmas," he said.
"A lot of companies will be shutting down, but you still need to make sure you have the latest updates. It is a good idea to set your machines up for automatic updates over Christmas and load all the latest patches."
Figures from IT security firm Message Labs have shown that in 2004 one e-mail in every 16 contained malicious code, compared to one in 33 in 2003. The most widespread outbreak of the year was W32/MyDoom.A in January.
Sophos, using a different measure of activity, found the most active virus to be Netsky-P, which accounted for almost a quarter of all virus incidents reported.
The mass-mailing Netsky-P and Zafi-B worms have been battling it out for the top spot for most of the second half of the year, and internet worm Sasser disrupted thousands of businesses and home users in May.