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termed 'automata'. He argued that the reproduction process for such automata would be fairly simple.

Later, in the 1960s, before the advent of computer games, university engineering students sometimes amused themselves by seeing who could write the shortest program that could reproduce an exact copy of itself. These were called 'self-replicating programs', but van Neumann would have recognized them as versions of his concept of electronic automata.

The first experiments to use self-replicating programs for something useful were carried out at Xerox's Palo Alto Research Center in the late Seventies. Two researchers, John Shoch and Jon Hupp, devised what they called a 'worm' program to help with the management of the Center's computer network, which linked over one hundred medium-sized machines. They envisaged the program working automatically, archiving old files, making back-up copies of current files, running routine diagnostic checks; they felt the program could perform endless housekeeping tasks that the researchers at Palo Alto were too busy to keep up with. They called their new program a worm, the two later said, in recognition of their inspiration – a sci-fi novel by the English writer John Brunner, called The Shockwave Rider, published in 1975. Brunner's book heralded the existence of a program which he called a 'tapeworm', that reproduced itself endlessly and couldn't be killed off.

Something rather like that happened to Shoch and Hupp. Their worm program was expected to sit quietly on one computer during the day, then emerge at night to roam the computers in the Research Center, carrying out housekeeping chores.⁴ Because it worked only at night, sceptical colleagues nicknamed it the 'vampire program'.

In their first test, Shoch and Hupp left the worm program 'exercising' on half a dozen designated machines in the lab. It wasn't programmed to do anything; it was just expected to travel to those designated machines and leave copies of itself. The next morning, though, when the two arrived back at their office, they found the worm had escaped, and had rampaged through all the hundred-plus networked computers in the Center. More worrying, it had reproduced so quickly that it had brought every machine to a halt, seem-

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