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

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 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 then 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 of the viruses, while Gokar was the most widespread, said Graham Cluley, senior technology consultant at antivirus software vendor Sophos .

Redesi was sent out after the September 11 attacks on the USA, masquerading as a patch from Microsoft to protect against terrorist virus attacks. When opened, the attachment would be activated, but wouldn’t act immediately. Instead it lay in wait, to reformat a victim's hard disk drive on 11 November.

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

Vallor was arrested on Valentine's day last year after the US Federal Bureau of Investigation (FBI) 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 UK. The first was Christopher Pile, who was sentenced to 18 months in prison in 1995 for spreading several viruses.

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 intenet in February of last year and spread much quicker and further than all three of Vallor's worms combined, according to Cluley.

David Smith, writer of the Melissa virus, which is said to have caused over $80m in damage, was sentenced to 20 months in prison in the USA early last year.