Microsoft will pay a $US250,000 reward for information leading to the arrest and conviction of the person or persons responsible for releasing the MyDoom.B worm.
The offer is part of Microsoft's $5 million bounty program that rewards people for information relating to worm and virus authors. It was announced in November 2003.
The Mydoom.B worm is similar to the MyDoom.A worm that appeared last Monday, but additionally contains a scheduled denial of service (DOS) attack against Microsoft's website and a feature that blocks access to anti-virus websites on infected machines.
Residents of any country were eligible for the award, Microsoft said.
According to Microsoft, the attack against the www.microsoft.com website was scheduled for February.
Microsoft said it is working with the Federal Bureau of Investigation (FBI), the US Secret Service and Interpol in investigating the MyDoom.B worm, the release of which Microsoft described as a "criminal attack".