A reward of $250,000 (£172,000) has been offered by Microsoft to find who is behind the Downadup/Conficker virus.
Since it started circulating in October 2008 the Conficker worm has managed to infect millions of computers worldwide.
The software giant is offering the cash reward because it views the Conficker worm as a criminal attack.
"People who write this malware have to be held accountable," said George Stathakopulos, of Microsoft's Trustworthy Computing Group.
He told BBC News the company was "not prepared to sit back and let this kind of activity go unchecked".
"Our message is very clear - whoever wrote this caused significant pain to our customers and we are sending a message that we will do everything we can to help with your arrest," said Mr Stathakopulos.
Arbor Networks said as many as 12 million computers could be affected globally by Conficker/Downadup since it began prowling the web looking for vulnerable machines to infect in October.