On Thursday Citigroup announced that hackers had breached its systems in May and accessed personal data from 200,000 accounts â about 1% of its customers. The hackers managed to steal customer email addresses, contact information and account numbers, but Reuters reported that other information such as birth dates, Social Security Numbers and credit card expiration dates were not accessed. “We are contacting customers whose information was impacted. Citi has implemented enhanced procedures to prevent a recurrence of this type of event,” Citigroup spokesperson Sean Kevelighan, said. “For the security of these customers, we are not disclosing further details.” It is currently unclear who was responsible for the breach.