A computer containing MI5 anti-terror files has been stolen from a house after a window was left open.

The burglar stole the computer after climbing in through an open window of a house rented by the security services.

Officers believe it was an opportunist theft and that the house in Greater Manchester was not targeted.

Police said the files were encrypted - making them impossible for anyone to access them without the relevant security code.

A force spokesman said: "Shortly after 11.20pm police were called to a house in Greater Manchester, following reports of a burglary.

"An encrypted hand-held computer was stolen. It is believed the offender entered through an open window."

This latest breach of security comes days after an MI6 agent accidentally sold a digital camera on eBay containing images of terror suspects.

The new owner, who bought the camera for £17 on the auction website, discovered photos of terror suspects, their names and fingerprints and even images of rocket launchers and missiles.

The 28-year-old from Hemel Hempstead, Hertfordshire, only found the secret images when he downloaded his own holiday snaps from the Nikon Cool Pix device.

After telling local police, he was shocked when Special Branch officers arrived at his home days later to seize his new purchase.

The Ministry of Defence has admitted 658 of its laptop computers have been stolen over the past four years.

In June, a civil servant was suspended after leaving confidential documents, containing the latest intelligence on al-Qaeda, on a train seat.