American Express is writing to customers warning them that their account information may have been compromised in a data breach at a third party service provider.
The firm has filed a data breach notification filed with the state of Massachusetts confirming the hack on a service provider used by its travel services division, American Express Travel Related Services Company.
American Express Card account numbers and other information such as the expiration date, may have been compromised.
The firm is urging customers to review their account statements, adding that card members will not be liable for any fraudulent charges.
However, it has not revealed how many customers re affected, the identity of the hacked third party or when the attack happened.