Citigroup has revealed almost twice as many people were affected by the data breach in May than originally believed – some 360,000 North American customers. The company has reissued credit cards to some 217,600 customers.
The breach was made public in recent weeks but occurred on 10 May. Originally, 200,000 customers were said to be affected.
About 1pc of the bank’s card customers were affected by the breach on Citi Account Online, which was discovered last month during routine monitoring.
The customers’ data that has been viewed includes their names, account numbers, email addresses and contact information, Citi said.
Information such as birth dates, card security codes, card expiration dates and social security numbers have not been compromised.
The bank has more than 21m customers.
Citigroup is just one of a growing number of household names to be attacked by hacker groups.
Last night, the CIA was the latest to be hit in an attack by hacker group LulzSec in a spree of attacks that included the US Senate.
