On September 8, 2018, Marriott received an alert from an internal security tool regarding an attempt to access the Starwood guest reservation database in the United States. Marriott engaged security experts to help determine what occurred. Marriott learned during the investigation that there had been unauthorized access to the Starwood network since 2014.
The company recently discovered that an unauthorized party had copied and encrypted information, and took steps towards removing it. On November 19, 2018, Marriott was able to decrypt the information and determined that the contents were from the Starwood guest reservation database.