Marriott says guests' names, loyalty account information and other personal details may have been accessed in the second major data breach to hit the company in less than two years.
Marriott said on Tuesday approximately 5.2 million guests worldwide may have been affected.
The information taken may have included names, addresses, phone numbers, birthdays, loyalty information for linked companies like airlines and room preferences.
Marriott said it's still investigating but it doesn't believe credit card information, passport numbers or driver's licence information was accessed.
Marriott said it noticed an unexpected amount of guest information was accessed at the end of February using the login credentials of two employees at a franchised property.
The company said it believes the activity began in mid-January.
Marriott has disabled those logins and is assisting authorities in their investigation.
The company didn't say whether the employees whose logins were used were suspected.
In November 2018, Marriott announced a massive data breach in which hackers accessed information on as many as 383 million guests.
In that case, Marriott said unencrypted passport numbers for at least 5.25 million guests were accessed, as well as credit card information for 8.6 million guests.
Australian Associated Press