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virus in March 1988 when he was twenty-four 'as an experiment'. He wanted, he said, 'to "say hello" to other computer users in my city. I never thought or expected it to spread nationwide and then world-wide. I was really surprised when my virus attacked the USA.'

If Denny was surprised, the computer industry was flabbergasted. Den Zuk was neither a particularly infectious bug, nor was it grown in a locale that could be said to be within the communication mainstream. Bandung, for all its undoubted charm, it not a city normally associated with high-technology industries. Denny's virus travelled simply because it got lucky.

Viruses are unguided missiles. It is just as likely that a bug launched from an obscure Indonesian city will hit targets in North America as one set off from, say, Germany. Nor is the sophistication of the bug any arbiter of its reach: Den Zuk was a simple virus, without any real pretension to what is known as an 'infection strategy'.

The universality of the PC culture is reflected in the provenance of viruses. In Britain, New Scotland Yard's Computer Crime Unit recently listed the country's most troublesome bugs. The viruses came from New Zealand, Taiwan, Italy, Israel (the Jerusalem virus), Austria, Pakistan (Brain), Switzerland, India and Spain – as well as a couple from the United States and even one that is believed to be from China.²

The increasing links between virus writers in different parts of the world is demonstrated by the growing number of adaptations of existing viruses. The Vienna virus, as has been shown, spawned a whole series of knock-offs, with slightly differing payloads or messages. So has the Jerusalem virus: there are now perhaps a hundred variants of the Israeli bug, all based on the single prototype. The knock-offs come from all over the world: Australia, Holland, the USSR (as was), Britain, South Africa, Czechoslovakia, Malaysia, Argentina, Spain, Switzerland, the US . . . The list is only slightly shorter than the membership of the UN. Some of the new viruses are just jokes, and play tunes; some are deliberately destructive.

Jerusalem's most fearsome variant comes from Asia. Called Invader, this bug first appeared in Taiwan in July 1990, where it is presumed to have been written. Within a month it had swept through the Far East and was reported to have reached North America. In

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