Millions of surfers have been warned about the latest Code Red II mutation that emerged into the wild last night.
Security experts said the infamous virus's latest variant - dubbed Code Red.d - was no more dangerous than the original, but warned internet users to be on their guard.
Code Red.d is almost identical to the original except for minor tweaks.
Modifications appear to have been made to change the variant's code signature in a bid to render it invisible to intrusion detection systems looking for the Code Red II string.
Roger Thompson, head of malicious code research at security firm TruSecure, explained that, in addition to other minor tweaks, an original code string - or "atom" - had been replaced with a series of underscore characters.
Graham Cluley, senior technology consultant at anti-virus software supplier Sophos, told vnunet.com that users who had already installed a patch protecting themselves from Code Red II would not have to worry about the latest virus variant.
"It's not very different from the original Code Red II. Users with Code Red II patched systems will also be protected from this latest threat," he said.
"We must stress that this shows how important it is to download the latest patches from Microsoft" he said.
Cluley added that surfers had only themselves to blame for the trail of destruction left by Code Red.
"If more people had downloaded the patch when Microsoft first warned them of the danger, we would not have heard hide nor hair of this virus. The patch was available before the worm even existed."
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