Records of women's smear tests and also of Aids tests have been accessed from the outside and tampered with, said Detective Inspector John Austen, head of the Yard's computer crime unit.
Mr Austen, who is also chairman of Interpol's computer crime committee, said that women who have had gynaecological treatment have been phoned by hackers, quizzed about intimate medical details and then subjected to obscene abuse.
His revelations came in an interview with the American news network NBC earlier this month which was never broadcast. ''Some of our hospital systems have been penetrated,'' he said. ''Hospitals of course hold lots of detail about patients and patient care. Some of the detail contains that of smear tests against women. We've had instances where those smear tests results have been attempted to be changed and pornographic telephone calls have resulted to women at home as a result of that activity.
''We've had other cases where organisations and haemotology departments have been conducting tests into diseases such as Aids where some of those results have been tampered with.''
Mr Austen said health care facilities tend to be ''soft targets'' because their primary concern is treating patients rather than protecting computer systems. ''One doesn't immediately think systems such as that should have a high degree of protection. But they do, because there are those in our society who get some sort of perverted fun out of other people's distress.''
He did not reveal which hospital records had been breached but Scotland Yard confirmed yesterday that officers in Croydon have investigated computer hacking offences earlier this month. The Department of Health said yesterday it did not have details of the breaches.
Mr Austen's claims highlight revelations in the Independent last week that hackers have taken secret information from British Telecom's main computer and stored it on the Internet, a world computer network available to 35 million people.
He said hackers had used the Internet to intrude into systems on military sites and commercial sites in the UK. ''We counted something like 5,000 to 10,000 over the last four years.''