NEW YORK ( TheStreet) -- Citigroup ( C) has confirmed that about $2.7 million was stolen from 3,400 customers in May following a major data breach.

Citi had had previously said that the data breach had exposed 360,083 bank accounts, revealing names, account numbers and email addresses of customers. Citi said other sensitive information including social security numbers, dates of birth, card expiration dates and card security codes had not been exposed.

However, it now appears that customers did suffer financial losses. A Citi spokesperson said he could not comment on how the money had been stolen, but that the breach itself had not contributed any information that was sufficient to perpetrate fraud.

Citi has said before that customers will not be liable for any fraud on their accounts and are "100% protected".

Citi has come under attack for failing to disclose the breach sooner. . The bank defended its response to the hack, saying it had immediately rectified the data breach upon discovery and had launched an immediate investigation to determine the number of accounts and information hacked.

--Written by Shanthi Bharatwaj in New York

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