A US district court in Seattle has sentenced a Minnesota teenager to 18 months in prison for unleashing a variant of the MSBlast.B worm, reported Xinhua.

Jeffrey Lee Parson, 19, was ordered to serve his time in a minimum security prison, participate in 10 months of community service, pay restitution and be placed under supervision for three years following the sentence.

Federal Bureau of Investigation (FBI) agents arrested Parson at his home in Hopkins, Minnesota, in August 2003, just two weeks after his "MSBlast.B" variant began to tunnel into Microsoft Windows-based computers.

The variant of the worm infected approximately 48,000 computers that had not used a security patch.

Parson pleaded guilty to damaging federal government computers with the virus. At the time of his plea, he faced a possible prison sentence of 10 years and a fine of $250,000.

But District Judge Marsha Pechman did not give the teenager the maximum sentence, saying Parson wrote malicious software and used it to attack other computers partly because of neglectful upbringing and supervision.

A hearing for the amount of restitution to be paid to Microsoft and others affected by Parson's Blaster variant will be held in February.

Microsoft's attorneys said that damages could easily amount to more than a million dollars.

Blaster and its variants are self-replicating Internet worms that bore through a security hole in Microsoft's Windows operating system, which is installed on more than 90 percent of the world's personal computers.