The Nyxem worm stormed to number four in this month's virus chart compiled by security firm Sophos, but it was old time viruses that made the biggest gains. 

Sober-Z topped the charts once again, despite a fix being available since November. Netsky-P made it back to number two, despite a cure being available for nearly two years, and Zafi-B, first detected in June 2004, has made a comeback at number three.

"Some of these worms have been around for years, and should act as a wake up call for businesses and users who don't have adequate protection," said Carole Theriault, senior security consultant at Sophos.

"These worms are simple to control as long as a consolidated solution is in place, and their spread would have been halted if antivirus updates were applied."

Sophos found 2,312 new viruses last month, and its research showed that one in 70 emails contains a virus.

The Sophos top 10 viruses in January 2006 cane be seen here.