SEATTLE (Reuters) - Prosecutors in Seattle said on Friday that they had arrested a juvenile for releasing a variant of the Blaster worm that devastated computers worldwide and targeted Microsoft Corp.'s MSFT.O computers.

The arrest of the juvenile, whose identity was sealed from the public, was for "intentionally causing damage and attempting to cause damage to protected computers," a federal offense, said John McKay, United States Attorney for the Western District of Washington.

"Computer hackers need to understand that they will be pursued and held accountable for malicious activity, whether they be adults or juveniles," McKay said in a statement.

Blaster and its variants are self-replicating Internet worms that bore through a Windows security hole.

Details of the investigation were also sealed, but authorities said the juvenile had released a variant of the Blaster worm called RPCSDBOT, which told infected computers to launch a denial of service attack on Microsoft's Web site.

The attack targeted a Microsoft update page that would have fixed the flaw, but Microsoft had changed its Web address in order to thwart the attack.

The Washington Cyber Task Force, which includes local law enforcement, the Seattle Division of the FBI and the Secret Service participated in the investigation with the assistance of Microsoft, McKay said.

The arrest comes a week after Jeffrey Lee Parson, a Minnesota teenager suspected of creating another variant of the destructive Blaster worm, was indicted in a Seattle court on one count of causing damage to a computer.

Parson, 18, a burly high school senior from Hopkins, Minnesota, has pleaded not guilty to the charge of intentionally causing or attempting to cause damage to a computer. He faces a maximum of 10 years in prison and a $250,000 fine if convicted.