The Love Bug, which brought corporate networks to a halt by raiding desktop address books and e-mailing hundreds of copies of itself to other users, cost companies an estimated £6bn last year.
But it will only be a matter of time before virus writers combine the ability of the Love Bug to reproduce on a massive scale with the devastating payloads seen in some other viruses, said Graham Cluley, technical director of anti-virus firm Sophos.
"I think within the next year we will see new viruses that propagate like the Love Bug but with far more vicious payloads," he said.
A combination of the Love Bug and the payload of the Chernobyl virus, which attempts to destroy the PC Bios, could put companies out of action for weeks.
"It is not difficult to change the payload for someone who has immersed themselves in the technology," said Rob Hailstone, director of software infrastructure research at IDC.
IT managers will face some difficult decisions as their companies begin to implement PKI and encrypted e-mail, said Cluley.
E-mail encryption technologies will allow viruses to escape detection in the network, leaving desktop anti-virus software as the sole line of virus defence.
Users will also need to consider virus protection for personal digital assistants and eventually wireless application protocol phones.