The inventor of the GoKar, Admirer and Redesi mass-mailing worms has been sentenced to two years in jail.
Simon Vallor, 22, from Llandudno in North Wales, had earlier confessed to creating the viruses, pleading guilty to charges brought under the Computer Misuse Act.
Judge Geoffrey Rivlin QC told the court that he had given the jail term as a deterrent to others.
"People who commit such offences are not just computer buffs or nerds sitting alone in their bedrooms obsessed with their computers," he told Vallor. "They also happen to be criminals who are difficult to detect, as they well know."
Vallor's viruses are thought to have attacked more than 27,000 computers in 42 countries.
He told police that he had not intended to do any harm, even though the viruses had destructive qualities. They were programmed to stop computers operating and, when infected computers were re-booted, the viruses would destroy material.
The case is one of a just a handful of successful prosecutions brought under the Computer Misuse Act.
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