A laptop containing personal information on about 600,000 people was stolen from an officer in the Royal Navy, the UK's Ministry of Defence revealed on Friday.
The laptop contained information about new and potential recruits to the Royal Marines, the Royal Navy and the Royal Air Force, and was stolen in Birmingham.
The stolen data includes passport details, national insurance numbers, family details and doctors' addresses for people who submitted an application to the forces, the ministry said. The laptop also contained bank details for at least 3,500 people.
"The Ministry of Defence is treating the loss of this data with the utmost seriousness," it said in a statement.
It is writing to people whose bank details were on the laptop and has notified the Association for Payment Clearing Services to watch for unauthorised access.
The ministry is investigating the theft with the West Midlands Police. The laptop was stolen on January 10, but the ministry said it didn't disclose the incident immediately for fear of compromising the investigation. It decided to go public with the loss after media reports surfaced about it on Friday, it said.
The laptop was stolen during the night from the car of a junior Royal Navy officer, who now faces a possible court martial, according to a report in the Times.
This is the latest in a string of data security lapses in Britain that have embarrassed the government and called into question its plan to create a central database of patient records for the National Health Service.
In November, Her Majesty's Revenue & Customs lost two CDs containing personal data on about 25 million Britons. The discs, which were encrypted and password-protected, were sent via interoffice mail and never arrived.
The following month, the Driving Standards Agency said it lost a disc containing the records of 3 million learner drivers, and soon after that the Department of Health said that nine of its regional NHS trusts had lost patient data, including medical records for about 160,000 children in East London.
Des Brown, the defence secretary, will make a statement to Parliament about the latest incident early next week, the Defence Ministry said. It did not say if the information on the Navy's laptop was encrypted or protected by password.
People who think they have been affected can send an email to email@example.com from Saturday at 10 a.m. UK time onward, the ministry said.