The latest variant of the Zafi worm was discovered on Wednesday and unlike the previous two variants, Zafi.C has been coded to launch a distributed denial-of-service (DDoS) attack against Google.com, Microsoft.com and miniszterelnok.hu, which is the Web site of the Hungarian Prime Minister.
The Zafi worm has evolved since it was first discovered in April of this year. Zafi.A contained Hungarian text and only tried to send itself to email addresses inside Hungary. Also, it did not contain a destructive payload. Two months later Zafi.B was released and this time the worm was able to terminate antivirus and firewall applications and 'speak' in numerous languages, including English, Spanish, Russian and Swedish.
Mikko Hyppönen, director of antivirus Research at F-Secure, said that if Zafi.C is worse than Zafi.B there could be trouble because the second variant has been in the company's top 20 virus list since it was released.
"Zafi.C might be bigger news as the previous variant of this Hungarian virus, Zafi.B, has been in our Top 20 for the past four months. However, so far we've received few reports of this virus."
Once active, Zafi.C scans the infected computer's Windows Address Book and hard drive for email addresses. It spreads by composing emails using a "complex set of rules" and sending them out with its built-in SMTP engine.
Paul Ducklin, head of technology at Sophos, Asia Pacific, told ZDNet UK sister site ZDNet Australia that the new variants are yet to have any affect on Australian users.
"The good news for Australia is that we haven't had any reports of any infections, so these viruses rate at the bottom of the prevalence scale. It's important to remember that around 1000 new viruses turn up every month -- approximately one every 45 minutes," said Ducklin.
Wednesday was a busy day for antivirus companies because apart from dealing with the new Zafi worm they also found a new version of MyDoom and another variant of the Agobot worm, which uses an Internet Relay Chat (IRC) server to give hackers remote access to infected systems.
Ducklin said the latest Agobot is the 359th variant.
Munir Kotadia reported from Sydney for ZDNet Australia. For more ZDNet Australia stories, click here.