The British Financial Services Authority is investigating the theft of laptop computer that may compromised the identity of up to 11 million people.

The computer was taken from a Nationwide Building Society employee's home in August, but Nationwide officials said they didn't inform customers until recently because they didn't wish to create undue anxiety, Sky News said.

Nationwide said the laptop contained customer information, but not material such as personal identification numbers, passwords or information about financial transactions.

The building society is writing to all of its customers about importance of security, Sky News said.