A senior company official conceded that it was still possible for any employee - temporary or permanent - to joyride across the system, which holds details of all BT's 20 million customers.
The Independent disclosed last week that hundreds of documents, giving unlisted numbers and addresses for the intelligence services, military facilities, 10 Downing Street and Buckingham Palace, had been leaked.
Asked by the Independent whether the company believed security on the computer was lax, the spokesman said: ''It is as secure as any system of its kind.'' He confirmed, however, that no secret numbers - those of the intelligence services, for instance - are ring-fenced from general access. BT was looking at ways of making that information more secure.
''The system is required to ensure that BT can operate. The stories in the Independent have highlighted what has been of some concern to us. As you know a high level investigation is now going on.''
BT confirmed temporary staff can gain access to the system by using the passwords of senior staff. It added: ''We do have policies laid down on passwords and breaches would be dealt with by dismissal and prosecution.''
John Major told the Commons last week that BT had told him the computer had not been ''hacked''. The BT spokesman said it would now investigate whether there had been hacking from outside. ''We will investigate and we will be very grateful for any information.''
The Prime Minister also told MPs that none of the confidential information taken off the computer had ever been on the Internet global computer network. On Friday the Independent found details of private telephone lines into Downing Street on the Internet.Reuse content