It looks like computer users are in for a tough year. Malicious code writers have already released several serious threats on the Internet. Antivirus software maker F-Secure on Friday rated four new Windows worms as Level-2 threats.

The Helsinki, Finland, company issued only 27 Level-2 alerts last year, and two Level-1 warnings, so having four serious worms unleashed close together within the first 10 days of the year is unusual. "The year isn't starting out great," said Fred Fondriest, director of business development for F-Secure. "If this continues, then we're in for a bad one."

The worms Lirva A and B, ExploreZip E and Sobig, reported Jan. 8 and 9, have infected computers, but the number isn't known. The worms rate a Level 2 because of their potential for damage, Fondriest said.

Lirva.A and Lirva.B enter computers as file attachments through E-mail, chat rooms, or the Kazaa file-sharing network. The worms are capable of disabling antivirus and security applications and stealing passwords. The latter are sent to an external E-mail address. A fan of Canadian rocker Avril Lavigne, who was nominated this week for five Grammy awards, apparently wrote Lirva, which spells Avril when reversed. When an unsuspecting computer user activates a Lirva worm, it tries to open Lavigne's official Web site.

ExploreZip.E is a variation of the first ExploreZip worm found in June 1999. The latest version arrives through an E-mail attachment, is undetectable by most antivirus programs, and destroys Microsoft Office documents and source-code files. It also will reply to unread E-mails, sending dummy responses with infected attachments.

Sobig, which has infected computers in 10 countries, is capable of installing a "backdoor" on a computer. A backdoor is a piece of code that gives the virus writer control of the infected computer and the ability to steal files.

The best defense against the latest threats is to update your antivirus software. "The hacker community is very active this year," Fondriest said. "Get updated. It's easy."