On Friday, Marriott revealed that its Starwood reservation system was breached, leaving more than 500 million guests’ information vulnerable to hackers.

The hospitality giant said guests’ personal information including payment information, name, address, phone number and date of birth have potentially been exposed.

Advertisement

“We deeply regret this incident happened,” Marriott CEO Arne Sorenson said in a press release.  “We fell short of what our guests deserve and what we expect of ourselves.  We are doing everything we can to support our guests, and using lessons learned to be better moving forward.”

Marriott learned of the cyber attack in September and discovered the breach impacted the Starwood reservation system earlier this month. Further investigation determined there was unauthorized access to the system since 2014.

Marriott is allowing guests to enroll in WebWatcher–a monitoring software– free of charge for one year. Guests from the United States who activate WebWatcher will also be provided fraud consultation services and reimbursement coverage for free.

The hack is one of a few recent cyber attacks targeting hotel companies. Just last year, Hyatt Hotels and InterContinental were both hacked.

Marriott International could not be reached for comment.