The forecast this year calls for more mass-mailing viruses that shut down corporate servers and more Trojan code that opens up backdoors into computer systems, according to security experts.

More mass-mailing Win32 viruses such as SirCam--which wreaked havoc on corporate networks this past summer--will continue to cause problems for corporations that fail to filter executable attachments at the e-mail gateway, according to Roger Thompson, director of malicious code research at TruSecure Corp., a security watch guard organization.

The SirCam worm, which scoops up documents in an infected PC and e-mails them to people in the user's address book, was No. 2 on Computer Associates' list of the top ten viruses for 2001, said Ian Hameroff, director of antivirus solutions at the software maker.

Both users and vendors will have to up the ante this year to thwart virus outbreaks since the level of sophistication exhibited by virus writers continues to rise dramatically, Hameroff said.

TruSecure's Thompson foresees more remote-access Trojan or backdoor programs plaguing consumers and businesses. Virus writers will continue to disguise this malicious code, which lets hackers gain control of infected systems, as "adult" movies and then post them to pornography news groups where unwitting participants will download and spread them.

Experts also expect to see more Internet worms such as Code Red and viruses such as Nimda, which can be spread through e-mail attachments, shared network files and infected Web sites.

Roughly 200 to 300 macro and script viruses are expected to emerge per month, Thompson noted. However, none of these will have any measurable impact since major antivirus programs will detect most of them.

Experts advise users to continue to place filters on e-mail gateways as well as to stay current with security patches and antivirus software.