Internet worms, which at first were thought to be dormant, are spreading around the world after incubating in areas such as Latin America, where antivirus (AV) protection is less stringent.
AV vendors are warning companies to make sure their software is up to date after the discovery of the internet worm Hybris, which like the virus Navidad, has seen its risk category upgraded.
Alex Shipp, AV technologist at application service provider MessageLabs, which scans email to protect customers from viruses, said that so far, his company had intercepted 154 copies of Navidad and four of Hybris. Both viruses have mainly been received from South America.
"Viruses like these are bubbling around in countries such as Brazil, where protection is less good, until they reach a large enough population to reach critical mass," said Shipp. "Once people with contacts overseas are infected, the viruses can then spread rapidly."
The issue is important because although protection has been available for some time, the Navidad virus struck 10 of the Fortune 500 companies in the US last week and has spread to the UK.
AV specialist Kaspersky Labs also said it had discovered five versions of the Hybris worm, which is particularly active in South America, and that it had been "inundated" with reports from users of what it described as "a highly sophisticated virus".
Hybris, which works only on Windows systems, spreads by attaching itself to infected emails. When a recipient executes the attached file, their PC becomes infected.
To spread, the worm infects the WSOCK32.DLL library and the Windows function that establishes a network connection. It scans for email addresses and then sends copies of itself to those addresses.
However, Graham Cluley, senior technology consultant at AV company Sophos, described Hybris as "small scale".
He said that end-users who practice "safe computing", which involves updating AV software and not opening suspicious attachments, would already be protected. "The telephones at Sophos are not exactly buzzing with this one," said Cluley.
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