California-based Panda Software said the spread of viruses and the variants "has reached epidemic proportions worldwide."

In the wake of the Mydoom outbreak, described as the worst in Internet history, Panda said there are several versions of the Netsky virus and the Bagle worm spreading quickly.

"They are all spreading at an alarming rate and causing an increasing number of incidents around the globe," Panda said. "According to the data collated by PandaLabs, there are now millions of infected e-mails in circulation."

The British firm mi2g called the latest outbreak a "tsunami" of malicious computer code, or malware, saying it is "overwhelming both its victim organizations as well as anti-virus toolkit companies and security professionals across the world."

Most security companies, Internet service providers and systems administrators have been severely overworked since the initial outbreak of Mydoom in late January, mi2g said.

The company said the latest outbreaks appear to mark a shift from adventurous teens to criminals seeking to make money through various schemes, including one called "phishing" to obtain credit card or financial information.

"This is not the activity of hobbyists but organized criminals," mi2g said.

This epidemic "is particularly worrying for companies, as all the viruses propagate aggressively, meaning that they can rapidly collapse corporate networks," Panda said in a statement. "At present some 95 percent of infected computers belong to companies."

Panda said Netsky.D is proving to be the most dangerous of all of them, spreading the fastest.

According to Luis Corrons, head of PandaLabs, "The idea that an epidemic is caused by a single virus clearly needs reconsidering. Virus creators are aware of the effectiveness of launching waves of malicious code and the increased probability of infection, and so we can expect to see more of these tactics in the future."

MX Logic, a security firm based in Denver, Colorado, said the Netsky.D worm "has reached a critical threat level, with one in every 71 e-mails infected by the worm."

"The first two months of this year have been marked by an unrelenting onslaught of mass mailing worms and their variants, including Mydoom, Mydoom.F, Bagle and Netsky.D. We are convinced that the frequency and potency of mass mailing worms and their variants is likely to increase -- making it critical that email users take every precaution to protect their inboxes," said Scott Chasin, chief technology officer, MX Logic.

Netsky.D does not delete files or damage computers, but contaminated computers played a jingle for three hours Tuesday morning.

"The author may be amused by the thought of an office full of infected PCs, all beeping away," said Graham Cluley of the software firm Sophos. "But the Netsky worm causes real harm by clogging up email systems and making unauthorized changes to computer systems."

Over the past days, virus fighters have battled a number of new releases of the Bagle and Netsky Internet worm families, and on Tuesday afternoon some 10 percent of all e-mails in Europe were contaminated by bugs, statistics showed.

In contrast to most other viruses, Netsky.D does not have an expiration date, and it will therefore remain a menace for some time to come, experts pointed out.

TERRA.WIRE