DETROIT - Marriott International said 5.25 million unencrypted passport numbers were stolen in the data breach disclosed in November.
The origin of the data breach is unknown, but China is seen as the likely origin of the cyberattack.
Cybersecurity experts said the compromise of the passport information is historic and impacted customers are exposed to cybercrime and economic espionage.
The passport numbers, paired with arrival, departure and reservation date information, could allow nations to track the movements of key government and business executives.
Marriott said it uncovered unauthorized access that's been taking place within its Starwood network since 2014.
What does this mean for you?
Guests' names, phone numbers, email addresses, passport information and credit card numbers and expiration dates may have been taken.
The hotel chain said the hack affected its Starwood reservation database, a group of hotels it bought in 2016 that includes the St. Regis, Westin, Sheraton and W Hotels.
The two Michigan hotels included in this breach are The Westin Book Cadillac Detroit hotel and the The Westin Detroit Metropolitan Airport hotel.
Data from more than 6,700 hotels around the world have been compromised. The hotel chain is offering some level of credit monitoring for those affected, but it's unclear how extensive it will be and how it will work to protect those affected moving forward.
A website and call center for anyone who thinks that they are at risk was set up by the chain.
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