IT security experts have increased the threat rating of the newly discovered Bagle.BC infection to 'Red Alert' as the worm continues to spread rapidly worldwide, causing more and more incidents.

Panda Software reported that, just a few hours after Bagle.BC first appeared, it has entered the top half of the ranking of the most frequently detected viruses by the firm's online antivirus scanner.

The number of incidents is expected to continue increasing and new variants are likely to emerge over the next few hours, security experts have warned.

"This has prompted Panda Software to declare a Red Virus Alert as a preventive measure, so that all users can protect themselves against these worms and prevent their computers from being infected," the security firm said.

"Similarly, companies also risk their communications being slowed down by the large number of emails that mail servers will have to process."

The danger has been further compounded by the arrival of two previously undocumented mutant strains of the virus, dubbed Bagle.BD and BE.

The new variants are very similar to Bagle.BC, which spreads via email, networks and P2P applications including Kazaa.

However, they do have some differences, such as the number of files they generate on infected computers.

The new Bagle worms share the fact that they have been designed to end the processes belonging to antivirus and security applications running in memory.

Luis Corrons, head of PandaLabs, explained that the objective of the authors of the worms is to release the maximum amount of malicious code to increase the probability of computers being hit by one of them.

"This is a technique that is being used more often," he said. "Virus creators know that the reaction time to new threats is critical, so the faster they can release various viruses the easier it is for users to take too long to update their system."