A man works on a new Marriott sign in front of the former Peabody Hotel in Little Rock, Arkansas. Marriott says the information of up to 500 million guests at its Starwood hotels has been compromised. Credit: Danny Johnston | AP

Marriott International revealed Friday that a massive data breach may have exposed the personal information of up to 500 million guests.

The data breach involved personal information mined from the reservations database for Starwood hotels, one of Marriott’s subsidiaries. An unauthorized party had accessed the database since 2014, officials learned, and was copying encrypted information. The hotel giant said the breach included names, email addresses, passport numbers, and possibly credit card numbers as well.

“We deeply regret this incident happened,” Arne Sorensonm, Marriott’s chief executive said in a news 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 said it reported the breach to law enforcement and is also notifying regulatory authorities.