Some American Express customers' data was compromised as a result of a third-party security breach.

The security breach occurred at a service provider that provides customers with airline, hotel and other booking services using an online portal.

A hacked third-party intermediary processor processed American Express Card member data. The hacked data included current or previously issued Amex card account numbers, customer names, and other information such as card expiration dates.

The company advises customers to be vigilant in monitoring their accounts for fraud and suspicious transactions.

Amex has informed customers that it will not be responsible for any fraudulent transactions on their accounts. Amex recommends that customers analyze their account statements over the next 12 to 24 months and turn on instant alerts through the company's mobile app to receive notifications of possible suspicious activity.