Microsoft has taken the unprecedented step of offering a $500,000 reward for information relating to the capture of two virus writers.

The authors of the SoBig and MSBlast viruses, which caused havoc to businesses' and individuals' computers running on the software company's Windows operating system during August and September of this year have never been found. Instead only a handful of virus writers who produced variants of MSBlast have been charged.

Collaborating with the FBI, US secret service officials and international crime force Interpol, Microsoft pledged a $250,000 reward per virus writer. It is the first time the company has ever put up money for virus authors.

"These are not just internet crimes these are real crimes that hurt a lot of people," said Brad Smith, Microsoft's general counsel, in a press statement.

MSBlast, also known as the LovSan worm, spread via email. Once installed the virus searched for other vulnerable machines to infect, causing heavy traffic problems across hundreds of networks. No individual culprit or group has ever been found.

The more traditional SoBig virus was immediately blamed on a group, although the organisation responsible has never been found. Transferred via email, the virus hunted for contact details in address books and sent itself on to the ones it found.

Microsoft hopes the reward will spark a media fury and encourage anyone with information to step forward.

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