A USB stick containing data on police operations has been stolen from an officer's home in Oldham.
A spokesman for the Greater Manchester Police, for whom the officer works, explained that the memory stick contained information about Greater Manchester Police operations and that the force is taking this loss of data very seriously.
The spokesman added that a dedicated team of officers is working to identify the burglars and recover the memory stick.
Assistant Chief Constable Garry Shewan denied reports that details on police informants had also been lost, but admitted that the private information of at least one member of the public may have been on the device.
He said: "Any suggestion this memory stick contained lists of names of people who 'tipped off' police is inaccurate. We know what is on the device because the officer has told us, and so far we have only had to speak to one member of the public whose personal information may have been compromised."
The Information Commissioner's Office (ICO) is aware of the loss, and is currently investigating it.
An ICO spokesman said: "We will be making enquiries into the circumstances of the alleged breach of the Data Protection Act before deciding on the necessary course of action."
Shewan said the force will be tightening up its data security practices as a result of the theft.
"Greater Manchester Police is reinforcing to officers and staff the importance of keeping information secure at all times. We expect all officers and staff to adhere to rigorous standards with regard to confidential and sensitive documents."