Greater Manchester Police has been forced to shut down their network and cut links to the Police National Computer, after the Conficker worm struck again.
Police officers were left relying on neighbouring forces to access information from the national criminal records database, as IT staff battles to clear the infection.
"It is not destructive and no data has been lost but due to the speed it had spread and we temporarily cut off our access to the Police National Computer and other Criminal Justice systems to prevent further infection,” said Thompson.
The Assistant Chief Constable said the police invoked contingency plans "to ensure this did not affect our service to the communities of Greater Manchester. It is still not clear where the virus has come from but we are investigating how this has happened and are taking steps to prevent this from happening again," he added.
In June 2009 Manchester City Council was struck by a Conficker outbreak that cost it £1.5 million to clear.
The council IT department spent £1.2 million fixing the problem, including £600,000 on external IT consultants, including Microsoft staff, £169,000 on staff to process a backlog of benefits claims and council tax bills, and compensation payments to families awaiting benefits. In addition it cancelled parking fines and bus lane tickets as systems were taken off line to be checked.
Investigators are leaning toward blaming the outbreak on an infected memory stick that someone plugged into a computer on the network.
The Conficker worm, which was discovered in November 2008, continues to morph and spread, with some estimates putting its sphere of influence at 7 million computers.
Despite its size, the botnet it controls has rarely been used and usually not in very large numbers. Some investigators theorize that the author doesn't want to attract even more attention, so is keeping the botnet's activity to a minimum.