Personal information including names, addresses, dates of birth, social security numbers, driver's licence numbers and in some cases, credit account information was accessed by "unauthorised persons".

The incident was first reported by The Breach Blog which provides links to a letter sent by the bank to New Hampshire Attorney General Kelly Ayotte.

In the letter Wells Fargo says it was notified by a reseller of consumer data - including credit bureau data - of suspicious transactions made using its own access codes.

The bank says "a significant number of unauthorised transactions" had been made using the codes, but it does not yet know how the codes were compromised.

In a letter to customers Well Fargo says it is providing affected customers with a free one year subscription to credit monitoring services.

Wells Fargo has been hit by a number of security breaches over the past few years. In 2006 a computer containing confidential information on mortgage customers was reported as missing; in 2004 four computers containing confidential data on Wells Fargo customers was stolen from the Atlanta offices of document processing vendor Regulus Integrated Solutions; and in 2003 thieves stole a computer containing Wells Fargo customer data from an analyst's office in Concord, California.

News of the latest Wells Fargo breach comes after reports of the theft of computer equipment containing confidential data from a Vancouver branch of TD Canada Trust.

The bank told reporters last week that the stolen equipment may have contained names, addresses, dats of birth, social insurance numbers, account numbers, bill payment details, transactions and balances.

Meanwhile earlier this month two men were arrested by the FBI on charges related to the illegal access of computers containing personal identification information of Countrywide Home loan customers and the illegal sale of the data.

Rene Rebollo, 36, is a former employee of Countrywide Home Loan and stands accused of giving out account to third parties over the course of two years while he was employed as a senior financial analyst at the firm's subprime mortgage division. Rebollo allegedly saved data to his personally-owned flash drives and left the Countrywide Home Loan premises with the intent to sell the data.

The FBI also arrested Wahid Siddiqi, 25, who allegedly purchased the data from Rebollo.