Paul Bedworth, now 19, was said to have used a pounds 200 microcomputer at his home in Ilkley, West Yorkshire, to dial up the Financial Times's network and introduce a rogue program into the high-tech system, the court was told.
In the process he allegedly deleted an important file, landed the organisation with a bill of several thousand pounds and forced computer managers to take a 'crucial' system out of service while the damage was repaired.
Tony Johnson, the FT's head of computers, said he discovered the electronic intrusion in May 1991. He found that the system, which held important statistics including the share index and was essential to the paper's daily production, had been tampered with.
A continual dialling program, which scanned computer networks, had been introduced. 'There was an outgoing call dialling every second - there were thousands of calls made,' he said. A password file was also deleted.
Mr Johnson told the court it landed the FT with a telephone bill of pounds 705. But the total cost to the FT was much higher - pounds 24,871. 'We had to take out the affected computer and rent another. It caused considerable disruption,' he said.
Ian Macdonald QC, for the defence, asked Mr Johnson: 'You need special cards to get in even if you are a visitor, but so far as the computer is concerned, that did not have the same security?'
Mr Johnson said: 'It had a level of security where people could access only to deliver information to the computer.' He disagreed when Mr Macdonald suggested: 'The physical security simply was not matched (by the computer)?'
Mr Bedworth, now studying artificial intelligence at Edinburgh University, denies three conspiracy charges under the Computer Misuse Act 1990, alleging unauthorised modification of computer information, securing unauthorised access to computer information and obtaining telegraphic services unlawfully.
The trial continues today.