The world's largest hotel chain, Marriott International Inc., said Friday that personal information of up to 500 million guests has been stolen in a database breach since 2014.

For about 327 million of those guests at its Starwood brand hotels such as Sheraton and Westin, leaked information includes names, mailing addresses, phone numbers, email addresses, passport numbers and dates of birth.

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For some, the stolen information includes credit card numbers and card expiry dates, it said. While credit card numbers were encrypted, Marriott said it "has not been able to rule out the possibility" that data needed to decrypt the card numbers were also taken.

The hacked database contained information relating to reservations made on or before Sept. 10, Marriott said. The hotel chain began sending emails Friday to affected guests.