In a bid to catch virus writers, Microsoft is offering up to $5m (£2.9m) in rewards to individuals who turn in the creators of worms, viruses and other types of malicious internet code.

The cash, part of the software giant's AntiVirus Reward Programme, is designed to help law enforcement agencies attract information that results in the arrest and conviction of those responsible for launching malicious code.

Microsoft said the reward is open to residents of any country, because internet viruses affect the internet community worldwide.

As part of the scheme, the company announced that an initial bounty of $250,000 was up for grabs by anyone providing information leading to the arrest and conviction of those responsible for unleashing the MSBlast.A worm.

Although two arrests were made in connection with the B and C variants of the MSBlast worm, the creators of the original worm - designed to attack Microsoft's Windows Update website this summer - remain at large.

A second $250,000 has been offered for information that leads to the arrest and conviction of those responsible for unleashing the SoBig virus.

This virus, the first variant of which was detected in January 2003, attacked individual machines and emailed itself to each address in the computer's contact list.

The SoBig.B and SoBig.C variants made messages appear as if they had come from official Microsoft email addresses. No arrests have yet been made in connection with SoBig.

"Malicious worms and viruses are criminal attacks on everyone who uses the internet," said Brad Smith, senior vice president and general counsel at Microsoft.

"Even as we work to make software more secure and educate users on how to protect themselves, we are also working to stamp out the criminal behaviour that causes this problem.

"These are not just internet crimes, cyber-crimes or virtual crimes. These are real crimes that hurt a lot of people. Those who release viruses on the internet are the saboteurs of cyberspace, and Microsoft wants to help the authorities catch them."

Representatives of three law enforcement agencies - the Federal Bureau of Investigation, the Secret Service and Interpol - attended the reward programme's launch.