Citigroup said computer hackers breached the bank's network and accessed data on hundreds of thousands of bank card holders.
In the latest high-profile cyber attack, the bank said about 1% of its card customers were affected by the breach, which the Financial Times said had been discovered in May during routine monitoring.
The names of customers, account numbers and contact information, including email addresses, were viewed, Citi said.
However, it said other information such as birth dates, social security numbers, card expiration dates and card security codes (CVV) were not compromised.
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