LONDON — A computer containing banking security details of more than 1 million people has been sold on eBay for $64, bank officials said Tuesday — the latest in a series of losses of personal data in the U.K.

The computer contained account numbers, passwords, cell phone numbers and signatures. It belonged to MailSource UK — an arm of Graphic Data, an archiving company that holds financial information for Royal Bank of Scotland, NatWest and American Express.

The security breach became known when the computer's buyer found the information and contacted authorities.

Britain's Information Commissioner's Office has launched an investigation into the incident. Banks in Britain are obligated under the Data Protection Act to secure personal information. But banking and other highly sensitive information is being lost with increasing frequency.

Last year, Nationwide Building Society was fined nearly $2 million after a laptop containing private customer data was stolen from an employee's home.

Last week, a contractor lost a memory device containing information on prison inmates in England and Wales.

In June, two sets of secret government files on terror tactics were left on commuter trains.

In January, a computer containing sensitive details on 600,000 prospective military recruits was snatched from the car of a Royal Navy recruitment officer in central England.

And in November, tax officials also admitted they had lost computer discs containing banking information on 25 million people — nearly half the country's population.

The Royal Bank of Scotland said it was looking into how the information in the most recent incident wound up on eBay.

"We take this issue extremely seriously and are working to resolve this regrettable loss with Graphic Data as a matter of urgency," Royal Bank of Scotland said in a statement.

American Express also issued a statement saying an investigation was under way to determine whether any of its customers were affected.

Telephone calls to both companies were not immediately returned.

A MailSource employee removed the computer from the group's storage facility and sold it, Graphic Data said.

"The IT equipment that appeared on eBay was neither planned nor instructed by the company to be disposed," said Nicole Morgan, spokeswoman for Graphic Data, based in Shoeburyness, England. "Investigations are ongoing to find out how this equipment was removed from one of our secure locations."

Jenny Thomas, a spokeswoman for eBay, said the item should have never been sold on the auction site.