Citigroup suffered about $2.7 million in losses after hackers found a way to steal credit card numbers from its website and post fraudulent charges.
Citi acknowledged the breach earlier this month, saying hackers had accessed more than 360,000 Citi credit card accounts of U.S. customers. The hackers didn't get into Citi's main credit card processing system, but were reportedly able to obtain the numbers, along with the customers' names and contact information, by logging into the Citi Account Online website and guessing account numbers.
Until now, it wasn't clear how much -- if any -- fraud had occurred as a result of the theft. But Citi confirmed Friday that there were losses of $2.7 million from about 3,400 accounts.
The bank has said its customers will not be liable for the losses.
Citi learned about the hack on May 10 and began notifying customers on June 3. The bank said other sensitive data, such as Social Security numbers, birthdates and the cards' CVV (Card Verification Value) security codes used for online transactions, were not taken.
In addition to the fraud losses, Citigroup will have to pay the cost of notifying customers and reissuing credit card numbers for the 360,000 affected clients. The Ponemon Institute has estimated the average cost of a data breach at $214 per compromised record. By that yardstick, the breach would cost the bank $77 million.