Marriott International said early Friday that data on roughly 500 million customers staying at Starwood hotel properties had been compromised in a breach that gave unknown attackers access to the Starwood network since 2014.

The company said it 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 hotel giant said that on September 8, 2018, it received an alert from an internal security tool regarding an attempt to access the Starwood guest reservation database. The company said it “quickly engaged leading security experts” to conduct an investigation, which found that there had been unauthorized access to the Starwood network since 2014.

“Marriott 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 it was from the Starwood guest reservation database,” the company said in a breach disclosure.

According to the company, customers who made a reservation on or before September 10, 2018 at a Starwood property likely had their information compromised, which the company broke down as follows:

For approximately 327 million of these guests, the information includes some combination of name, mailing address, phone number, email address, passport number, Starwood Preferred Guest (“SPG”) account information, date of birth, gender, arrival and departure information, reservation date, and communication preferences. For some, the information also includes payment card numbers and payment card expiration dates, but the payment card numbers were encrypted using Advanced Encryption Standard encryption (AES-128). There are two components needed to decrypt the payment card numbers, and at this point, Marriott has not been able to rule out the possibility that both were taken. For the remaining guests, the information was limited to name and sometimes other data such as mailing address, email address, or other information. Marriott reported this incident to law enforcement and continues to support their investigation.

Marriott completed its acquisition of Starwood Hotels & Resorts Worldwide to create the worlds’ largest hotel company.

Starwood brands include: W Hotels, St. Regis, Sheraton Hotels & Resorts, Westin Hotels & Resorts, Element Hotels, Aloft Hotels, The Luxury Collection, Tribute Portfolio, Le Méridien Hotels & Resorts, Four Points by Sheraton and Design Hotels.

Starwood branded timeshare properties were also impacted by the incident.

Marriott said it was working to phase out Starwood systems and accelerate ongoing security enhancements to its network.

Shares of Marriott International are trading down roughly 6% in pre-market trading at the time of publishing. 

Via:  securityweek