AmEx card details were exposed in a third-party data breach

The company has filed a data breach notification with the state of Massachusetts confirming the hacking of 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 expiration dates may have been tampered with.

The company urges customers to check their statements, adding that cardholders will not be held liable for fraudulent charges.

However, it was not disclosed how many customers were affected, who the hacked third party was, and when the attack occurred.