Hackers exposed the names and account numbers of 210, 000 Citibank account holders last month, the BBC reports. The bank is facing severe criticism for its failure to inform customers about the breach sooner. A Citi spokesman told Reuters news agency that the company is contacting customers whose accounts were leaked, while working hard to prevent another breach from occurring. Citi officials encouraged customers to be on “high alert” for future scams. The identity of the hackers and how they managed to infiltrate Citibank’s system remains unknown.