Marriott - which owns Starwood hotels - announced that the Starwood guest reservation system had been hacked in a breach dating back to 2014.
Marriott has advised that the exposed information includes names, phone numbers, email addresses, passport numbers, dates of birth, credit card numbers and expiration dates were potentially compromised.
Marriott said it will start emailing users who were impacted and that it has set up a website https://answers.kroll.com/ with information about the breach.