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 company says.
The offer is part of Microsoft's $5 million bounty program to reward people for information relating to worm and virus authors.
The Mydoom-B worm is similar to the Mydoom-A worm that appeared on Monday, but additionally contains a scheduled denial of service attack against Microsoft's Web site and a feature that blocks access to antivirus Web sites on infected machines.
Both Mydoom variants target computers running Microsoft's Windows operating system. The worms spread through infected e-mail file attachments and the Kazaa peer-to-peer network. Mydoom quickly spread worldwide, infecting between 400,000 and 500,000 computers as of Thursday, according to Network Associates.
Microsoft first unveiled its bounty program last November, calling viruses and worms "criminal acts" and pledging $5 million for bounties to catch the authors of virulent worms and viruses. So far, Microsoft has offered bounties of $250,000 for information leading to the arrest and conviction of the individuals who created the Blaster and Sobig worms, which appeared last August.
However, it has not attached a bounty to any other worm or virus outbreak since then, leaving much of the $5 million untouched.
On Tuesday, Mike Nash, corporate vice president of Microsoft's Security Business Unit, said that a bounty was "possible" in the case of the Mydoom author.
Microsoft considers a number of factors before it decides to offer a bounty, including the number of systems infected by the worm and the amount of damage caused, Nash said.
The company also looks at the severity rating assigned to worms and viruses by antivirus companies such as Symantec and Network Associates' McAfee antivirus unit, a company spokesperson says.
Residents of any country are eligible for the award, Microsoft says.
According to Microsoft, the attack against the www.microsoft.com Web site is scheduled for February, which begins on Sunday.
Microsoft says it is working with the Federal Bureau of Investigation, the U. S. Secret Service and Interpol in investigating the Mydoom-B worm, the release of which Microsoft described as a "criminal attack."