Marriott said it determined on Nov. 19 that the information was from its Starwood database.
"The company has not finished identifying duplicate information in the database, but believes it contains information on up to approximately 500 million guests who made a reservation at a Starwood property," the company said in a statement.
For about 327 million of the guests, it added, the information includes some combination of a name, mailing address, phone number, email address, passport number, Starwood Preferred Guest account information, date of birth, gender, arrival and departure information, reservation date, and communication preferences.
There are some customers who may have also had their credit card information taken.
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