The records of 500 million customers of the hotel group Marriott International have been involved in a data breach.
The hotel chain said the guest reservation database of its Starwood division had been compromised by an unauthorised party.
It said an internal investigation found an attacker had been able to access to the Starwood network since 2014.
For about 327 million guests, the information included "some combination" of name, mailing address, phone number, email address, passport number, account information, date of birth, gender, and arrival and departure information.
It said some records also included encrypted payment card information, but it could not rule out the possibility that the encryption keys had also been stolen.
Starwood's hotel brands include W Hotels, Sheraton, Le Méridien and Four Points by Sheraton.