Citigroup's said that about one percent of customers had been affected, implying that around 200,000 had been affected.Citigroup released a letter to its customers implying that around 360,083 card accounts had been affected.
Citigroup now says it's replaced the cards of about 217,000 customers.
It seems California was the hardest-hit state, with about 80,000 affected accounts.
Citigroup has reiterated that the information taken won't allow hackers to access funds directly.
