Police were investigating the contents of a computer memory stick said to contain sensitive anti-terror material which was reportedly found in the street outside a police station.
The four-inch USB storage device was alleged to have contained more than 2,000 pages of confidential information, including strategies on combating terror attacks.
The memory stick was found by a 36-year-old businessman on a pavement outside the station in Stalybridge, Greater Manchester, said the Daily Star on Sunday.
It reported the device was emblazoned with the initials GMP POTU, standing for Greater Manchester Police Public Order Training Unit, and the files enclosed were produced by the National Police Improvement Agency on the subject of counter-terrorism and tactical deployment.
Names of officers, their ranks and divisions were also uncovered by the businessman when he fitted the stick into his laptop, the newspaper added.
Superintendent Bryan Lawton, of GMP's Specialist Operations Branch, said: "We are aware of an article relating to the finding of a memory stick belonging to GMP by a member of the public.
"We are currently looking into who this device belongs to, what information is contained on it and the circumstances surrounding its loss. As such it would be inappropriate to comment further at this time."