AMSTERDAM - A 22-year-old British man has been sentenced to two years in prison for creating and sending out three computer viruses, one of the toughest sentences given so far to a virus writer.

Simon Vallor of Llandudno, Wales, was sentenced Tuesday at London's Southwark Crown Court on three counts of releasing a computer virus contrary to section 3 of the U.K.'s Computer Misuse Act 1990. The man's computers have also been seized.

In December Vallor pleaded guilty to charges that he created and distributed the "Gokar," "Admirer" and "Redesi" viruses. He was released on bail until sentencing. The viruses Vallor created affected about 27,000 computers in more than 40 countries, according to court prosecutors.

All of Vallor's viruses spread via the Outlook address book. Redesi was the most destructive virus, while Gokar was the most widespread, said Graham Cluley, senior technology consultant at antivirus software vendor Sophos PLC in Oxford, England.

Redesi was sent out after the Sept. 11, 2001, attacks on the U.S., masquerading as a patch from Microsoft Corp. to protect against terrorist virus attacks. When opened, the attachment would reformat a victim's hard disk drive on Nov. 11, Cluley said.

Gokar had no destructive payload, but attempted to overwrite the home page if the system it hit was a Web server. Admirer just spread itself around as a Valentine greeting, Cluley said. Gokar hit Sophos' top-10 list of most commonly reported viruses in late 2001 and early 2002, he said.

Vallor was arrested on Feb. 14 last year after the U.S. Federal Bureau of Investigation tipped off Scotland Yard's computer crime unit.

In court, Vallor said he wrote and sent out the viruses as an experiment to see if they would eventually spread back to him. In an interview with the BBC the Welshman said he did not think his viruses would spread.

Sophos' Cluley deems Vallor "quite a technical writer" who "knew what he was doing."

This is only the second time that somebody has been convicted for creating and spreading a computer virus in the U.K. The first was Christopher Pile, who was sentenced to 18 months in prison in 1995 for spreading several viruses, Cluley said.

The two-year sentence is tough, perhaps the toughest ever handed down against a virus writer, according to Cluley.

"It sends out a strong message to other virus writers," he said.

In comparison, Dutchman Jan de Wit, who created the Anna Kournikova e-mail worm, heard his sentence of 150 hours of community service confirmed on appeal last year. The Anna Kournikova worm hit the 'Net in February 2001 and spread much quicker and further than all three of Vallor's worms combined, according to Cluley.

The writer of the Melissa virus, David Smith, was sentenced to 20 months in prison in the U.S. early last year. The Melissa virus spread in 1999 and is said to have caused more than US$80 million in damage.