Since claiming that only one per cent of its 21 million customers were affected by the recently revealed cyber attack its suffered, Citibank has since revealed that as many as 360,000 of its customers accounts may have been compromised.

The figure was released yesterday and is nearly double the amount originally estimated by the bank.

The hack reportedly happened in May and exposed the names, account numbers and contact information of thousands of the bank's customers.

Citibank has since clarified that the hackers did not manage to obtain certain bits of key information like customers birth-dates or card security codes.

Since revealing the attack the bank has been under pressure to reveal further details. It only admitted the security breach weeks after the attack occurred and it was only this Wednesday that it chose to elaborate on its initial statement.

Since the breach, Citibank confirmed that is has reissued 217,657 credit cards to affected account holders.

The FBI along with numerous other law enforcement agencies have already been contacted and are reportedly, "working with" Citibank's own security team to investigate the hack.