A German youth has been given a 21-month suspended sentence after being convicted of creating the Sasser worm which crippled computers worldwide.
Sven Jaschan spent four days on trial
Sven Jaschan was found guilty of computer sabotage and illegally altering data, said a court official.
He evaded a jail term as he was tried as a minor since he was 17 years old when he wrote the worm.
Sasser wrought havoc when the Windows worm struck in May 2004, swamping net links and making computers unusable.
Jaschan had admitted to creating the worm at the beginning of his trial on Tuesday, reiterating a confession to authorities at the time of his arrest in May 2004.
His sentence fell far short of the maximum sentence of five years in jail that computer sabotage carries under German law.
"Sven Jaschan avoided a jail sentence by the skin of his teeth because he was arrested within days of his 18th birthday," said Graham Cluley, senior technology consultant for anti-virus company Sophos.
"However, in the grand scheme of the virus world, it's the organised crime gangs, which are increasingly emerging to make stacks of money through targeted attacks, that should be dealt the harsh sentences, over and above the dumb teenagers."
Jaschan was arrested in May following a tip-off passed to Microsoft which put up a cash reward of $250,000 for information leading to the arrest of whoever was behind the virulent worm.
The two individuals who helped identify the Sasser creator will share the reward now Jaschan has been convicted, said Microsoft.
"We're pleased that the author of the Sasser worm has admitted responsibility for the damage he caused and is being held accountable," said Nancy Anderson, deputy general counsel at Microsoft.
The Sasser worm infected PCs and systems running Windows 2000 and Windows XP across the world after making its first appearance on 1 May.
In the UK, the worm shut down the computers of the Maritime and Coastguard Agency, with staff returning to manual map reading.
It also hit about 1,200 PCs at the European Commission headquarters in Brussels, and allegedly wrecked Delta Airlines' systems in Atlanta for seven hours, leading to the cancellation of 40 flights.
Around the world, the Australian Railcorp trains stopped running because computer problems caused by Sasser made it impossible for drivers to talk to signalmen.
In Taiwan, more than 400 branches of the post office were forced to use pen and paper because Sasser crashed desktop computers.
Unlike many other viruses, Sasser made its way from computer to computer without help from users. It got into Windows computers by exploiting a programming bug in the operating system.
Although Microsoft had released a patch for this loophole on 13 and 28 April 2004, many companies had not applied this protection before Sasser struck.