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ation of vampire programs that were reproducing uncontrollably and monopolizing its resources.

The same attackers hit the MIT Media Laboratory in Massachusetts. Pascal Chesnais, who was working late in the lab, thought he had managed to kill off his mysterious intruders, then went to grab a meal. When he got back, he found that more copies of the invaders were coming in with his electronic mail, so he shut down his network connection for a few hours. Then, at 3.10 a.m., he sent out his own warning: ‘A virus has been detected at Media Lab. We suspect that the whole Internet is infected by now. The virus is spread by [electronic] mail . . . So mail will not be accepted or delivered.’

Just before midnight the rogue program had spread to the Ballistic Research Laboratory, an army weapons centre in Maryland. The managers at the lab feared the worst: they could be under attack from hostile agents. Even if that proved not to be the case, they didn’t know what the program was doing. It was certainly multiplying, that was clear, but it might also be destroying data. By the next morning the lab had disconnected itself from the network and would remain isolated for nearly a week. It wasn’t alone in disconnecting – so many sites attempted to isolate themselves that electronic mail (the usual channel of communication between computer operators) was hampered, engendering even more confusion about what was happening. At one point the entire MILNET system severed all mailbridges – the transfer points for electronic mail – to ARPANET.

By midnight, the electronic freeways between the 60,000 or so interconnected computers on Internet and ARPANET were so clogged with traffic that computer specialists were roused from their sleep and summoned to their offices to help fight the attack. Most of them wouldn’t get back home until the next night.

At 3.34 a.m. on 3 November, shortly after Yee had sounded the first alarm, another message about the virus was sent from Harvard. This message was altogether more helpful: it wasn’t just a warning, it offered constructive suggestions. It outlined three steps that would stop the virus. The anonymous sender seemed to be well informed about its mechanisms. Because of the chaos on the network, though, the message wouldn’t get through for forty-nine hours.

In the meantime three ad-hoc response teams were being assembled