Microsoft will pay a $250,000 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 $5m bounty programme to reward people for information relating to worm and virus authors.
The Mydoom.b worm is similar to the MyDoom.a worm, but contains a scheduled denial-of-service (DoS) attack against Microsoft's website and a feature which blocks access to anti-virus websites on infected machines.
The attack against the www.microsoft.com website is scheduled for February.
Microsoft said it is working with the FBI, the US Secret Service and Interpol in investigating the MyDoom-B worm, the release of which Microsoft described as a "criminal attack".
David Legard writes for IDG News Service