The Bank of America has responded to the theft of personal information on 600,000 of its customers by upping its online security.

From next month, it will offer a new, optional, service called SiteKey that will make it harder for thieves to access Bank of America accounts.

SiteKey will recognise when a Bank of America account is being accessed via an unknown computer and generate a predetermined "challenge" question, adding an extra layer of security.

The software will also lets users choose a specific image - a photograph of a dog, for example - that can then be re-shown to users in order to reassure them that they are actually visiting the Bank of America website, and not another site masquerading as it.

The service will be rolled out as an optional feature for the bank's Tennessee customers, beginning next month. It will be available to all of the bank's 13.2 million online banking customers by October, said a spokeswoman. By then, it will most likely be mandatory.

The bank sort to play down the recent data theft however. "That had nothing to do with online banking," said the spokeswoman, without commenting any further on the matter.

The Bank of America was one of four banks targeted by the identity thieves, who managed to steal information on about 676,000 customers in total. Police have charged 10 suspects in the case, eight of whom are former bank employees.