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Prestel, they first see page one, which indexes all other services. Only the system manager can alter or update listings on this page. Triludan, exploiting his sysman status, made a modest change: he altered ‘Index’ to ‘Idnex’. But it was enough to signal to Prestel that its security had been breached. The other pranks had been worrisome, but altering the first page was tantamount to telling Prestel that its whole system was insecure. The company reacted quickly. It notified all its customers to change their passwords immediately. Then it altered the sysman codes, thus stopping Triludan and his friends from tampering with the system again.

Six months later Triludan was arrested. Though he had lost sysman status, he had continued hacking the system, using other four-digit combinations. He even continued to leave messages for the system manager, just to prove he continued to have access. But his games embarrassed Prestel and its owner, British Telecom, and the revelation that hackers had penetrated the Prestel system and broken into Prince Philip’s mailbox had proved irresistible to the British press, which had cheerfully hyped the story into page-one news. The royal connection ensured that the item got international coverage, most of it implying that hackers had breached royal security systems and read Prince Philip’s private and confidential electronic mail.²

To catch their hacker, Prestel put monitors on the incoming lines. These filtered all calls to the system, looking for unusual activity such as users trying different passwords or repeatedly failing to key in correct IDs. After watching the lines for a month, the authorities were convinced they had two intruders, not one. The first was calling from London; the second appeared to be dialling in from Sheffield. British Telecom then traced the two callers, and put supplementary monitors on their home lines.

Despite the fact that the company had evidence from the messages to the system manager that Triludan was still breaking into the system, they needed hard evidence. So they monitored the lines in London and Sheffield, noting the times the two callers dialled into Prestel and noting the traffic between the two. It was decided to mount simultaneous raids.

On 10 April 1985 a posse of three British Telecom investigators and four policemen raided the north London address they had

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