The image of the internet as a modern-day Wild West, complete with bounty hunters and Billy the Kid-type bad guys, was furthered today by the news that Microsoft has paid a $250,000 reward for help in tracking down a rogue teenaged programmer.

The software giant made the payment to two unnamed informers who helped trace the mastermind behind the Sasser internet worm, which infected computers around the globe and cost businesses million of dollars.

A German court last week gave Sven Jaschan, 19, a suspended sentence of 21 months after he admitted creating the malicious software from his bedroom in his parents’ house.

Sasser struck on May 1, 2004, and in less than a week hit as many as 18 million computers worldwide, forcing some businesses to shut in order to debug systems. Jaschan was arrested a week later and admitted to creating and releasing the worm.

Jaschan, who was tried as a minor, gave a full confession on the first day of his trial, admitting to charges of computer sabotage, data manipulation and disruption of public administration. The charges would normally carry a prison sentence of up to five years for an adult.

"He took malicious pleasure in making computers around the world crash," a court spokesman said.

The worm, which unlike a virus did not have to travel through e-mail but could propagate itself, moving to any unprotected computer linked to the internet, exploited a flaw in certain versions of Microsoft’s Windows operating systems - Windows 2000, Windows Server 2003 and Windows XP.

It forced infected computers into an unstoppable pattern of shutting down, then rebooting, rendering them useless.

"The Sasser worm is just one example of the speed at which a malicious code can spread across borders and how damaging it can be to industry and the public," David Gork, the director of Specialised Crimes at Interpol, said.

Two unnamed informants will share the $250,000 reward funded by Microsoft. The world’s largest software company said the payment would come from its anti-virus programme, which was established with Interpol, the FBI and the American Secret Service in November 2003 to provide incentives to help deter cyber-criminals.

In January, Jeffrey Lee Parson, 19, sentenced in US District Court in Seattle to a year-and-a-half in prison for releasing a variant of the Blaster worm that was used to attack more than 48,000 computers.

Jaschan, whose parents own a computer service company, now works for a German security software firm called Securepoint, which specialises in defence systems against viruses and worms.

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