An unemployed warehouseman from a seaside resort in north Wales was yesterday jailed for creating computer viruses with the potential to wreak havoc across the globe.

Simon Vallor, 22, was told that he was one of a new breed of criminal whose ingenuity allowed him to cause worldwide disruption on an "unimaginable scale".

Vallor's viruses, which he created on three computers in the bedroom of his family's pebbledash home in Llandudno, hit tens of thousands of computers in 46 countries.

Had he not been stopped by Scotland Yard's computer crime unit and the FBI, many more companies, organisations and individuals could have suffered, Southwark crown court, London, was told.

Vallor, who was jailed for two years, is only the second British man to be imprisoned for creating computer viruses.

The industry, which often accuses the courts of not taking the offence seriously enough, welcomed the sentencing.

Vallor's three viruses, GoKar, Redesi-B and Admirer, were spotted on the internet in December 2001 by the FBI's Newark field office.

Federal agents linked the viruses to someone who used the nickname Gobo and traced him to Britain. Scotland Yard's computer crime unit was then alerted.

GoKar was Vallor's most prolific virus. It appeared as an email on an user's computer with an "intriguing" single line of text such as: "If I were God and I didn't believe in myself would it be blasphemy."

When the email was opened the body of the text contained another apparently innocuous, if puzzling, message such as: "They say love is blind" or "Happy birthday, mine not yours."

Unbeknown to the user, the virus automatically sent itself off to every contact in the user's address book.

One anti-virus filter service alone stopped it 33,000 times. It had the potential to clog company computers and even force them to shut down email systems.

Scotland Yard claims that at one point GoKar was rated the third most prevalent virus of all time. But Vallor's other viruses, Redesi-B and Admirer, had the potential to be far more destructive.

Like GoKar, they looked like ordinary emails, again with inviting message lines.

Redesi-B purported to be a security update from one of the computer giants. The user was then invited to open an application that would help make their machine more secure. But, once this application was opened, it planted a virus in the computer with a delay mechanism.

After a certain period, the virus wiped off all material from the computer's hard disk. All the user would be left with was the message: "Bide ye the Wiccan laws ye must, in perfect love and perfect trust." Wiccan is a pagan religion that Vallor has claimed he has connections with.

The Admirer virus, which tempted users with messages such as "Secret admirer" and "Happy Valentine's Day", could also destroy material that had not previously been saved.

Ironically, the police raided Vallor's home, where he lives with his father and brother, on Valentine's Day. Vallor was in bed at the time.

Before his jailing, he said: "It was totally mind-blowing. One minute you're asleep, the next you've got Scotland Yard in your bedroom."

The police had taken about three weeks to trace him via his BT internet account. He told police his motivation was simply to see if he could do it.

In court his counsel, Grant Vanstone, depicted him as an "unremarkable young man" who left school with four GCSEs and worked for a time in a warehouse.

After his mother died during a holiday with relatives in 2000 he lost his job and became introverted and obsessed with computers.

He began writing GoKar on his birthday in 2001 because he was "feeling sorry for himself". Mr Vanstone said: "He was shocked when it spread as it did."

But after his arrest he did not appear contrite on his website, the Devil Within.

He wrote: "I caused no harm, endangered no one, hurt no one, damaged nothing yet I may very well be going to prison, while there are drink-drivers, rapists, even murderers who get let off."

The judge, Geoffrey Rivlin QC, made it clear that Vallor's sentence should be heeded as a warning by other virus writers. "People who commit offences such as this are not just boffins or nerds sitting alone with their computers," he said.

"They also happen to be criminals who are difficult to detect and have the capacity to cause disruption, consternation and even economic loss on an unimaginable scale.

"So many people rely on computers that any interference with that use must be regarded as a very serious matter." It was a crime, he said, which "cries out for a deterrent sentence".