For more than three days each
In the last year five British police forces have suffered major computer failures lasting three days or more as a result of malicious internet attacks.
The spate of intrusions by cybercriminals and the resulting outages was revealed recently by a senior authoritative source, who can't be identified because the disclosure was made under the Chatham House rule.
The source did not reveal which forces were the victims of the attacks or the method used.
The Association of Chief Police Officers, which coordinates police strategy nationally, declined to comment on the incidents.
Despite the official silence on the matter, the news of repeated breaches raises serious questions over the standard of police information security.
Virtually all of day-to-day police operations are dependent on IT systems such as the Police National Computer and the major incident coordination software HOLMES 2, as well as more mundane but vital human resources and equipment provisioning systems.
The databases used by police also contain untold sensitive and valuable personal information about suspects, witnesses and victims.