Microsoft is offering a $250,000 bounty on finding the creators of the damaging Downadup/Conficker virus.
Redmond is offering the reward as it views Conficker 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 the BBC Microsoft was "not prepared to sit back and let this kind of activity go unchecked".
"Our message is very clear, whoever wrote this code caused significant pain to our customers, and we are sending a message that we will do everything we can to help with their arrest," said Stathakopulos.