A hidden message in the latest version of Netsky read:
"Hey av firms, do you know that we have programmed the sasser virus?!?"
IT security experts said the claims are legitimate because the two worms share similarities in their coding.
The Sasser worm, which appeared on Friday, exploits a hole in versions of Microsoft Windows Server 2003, XP and 2000. Microsoft had previously released a patch for the bug, but many firms failed to implement the fix.
"The likely victims are home computers, and places that leave their systems wide open to the internet, such as universities," said Jay Heiser, senior analyst at IT risk management experts for TruSecure. "The overwhelming majority of corporate and government sites are well protected by their firewalls."