The teenage author of one of the most prolific and damaging computer viruses in recent times was given a suspended sentence by a German court today.

Sven Jaschan, 19, avoided a jail sentence because he created the "Sasser" and "Netsky" computer worms when he was only 17 years old and was tried as a minor.

Jaschan was given a suspended sentence of one year and nine months and was ordered to do 30 hours of community service by a court in Verden, a town in the north west of Germany.

The "Sasser" and "Netsky" internet worms zippped around the world last year, infecting millions of computers, causing them to repeatedly shut down and re-boot, making them impossible to use. The worms took advantage of a flaw in the Microsoft Windows operating system. Prosecutors said that they caused millions of pounds of damage.

The worms, which can travel from any computer as long as it is connected to the internet, affected companies and institutions across the world, including Delta Airlines in America, railway controllers in Australia, the European Commission in Brussels, Goldman Sachs and the British coastguard.

According to the British security company, Sophos, versions of Jaschan's viruses still account for over 25% of all virus reports it has received in the first six months of 2005. The "Netsky-P" form of the worm, which can pose as a Harry Potter computer game, is the second most widespread virus of the year to date.

Jaschan admitted his guilt to the court on Tuesday, repeating the confession he made to authorities soon after his arrest in May 2004.

He is currently working as an apprentice at a computer security firm, and was arrested last year at his computer in his mother's house in the central town of Waffensen. Police tracked Jaschan down after receiving a tip from an informant seeking the $250,000 reward offered by Microsoft for his capture.

Jaschan, described by the prosecution as a "computer freak", has said that his original intention was to design a worm to fight other viruses, such as the damaging "Mydoom" and "Bagle" viruses.

Graham Cluley, a senior technology consultant for Sophos, said that Jaschan's story is of the corruption of a promising computing talent.

"Sven Jaschan avoided a jail sentence by the skin of his teeth because he was arrested within days of his 18th birthday," said Mr Cluley.

"It's a sad story of how a young man with potential can make the wrong choices and end up disrupting millions of business and home computer users around the world.

"It's a shame that someone with such IT skills should turn to writing computer viruses to increase his self esteem, rather than doing something positive like developing computer games or an innovative website."

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