By MICHELLE CHAPMAN and MAE ANDERSON
Associated Press

NEW YORK (AP) - Hackers stole information on as many as 500 million guests of the Marriott hotel empire over four years, obtaining credit card and passport numbers and other personal data, the company said Friday as it acknowledged one of the largest security breaches in history.

The full scope of the failure was not immediately clear. Marriott was trying to determine if the records included duplicates, such as a single person staying multiple times.

It was also unclear what hackers could do with the credit card information. Though it was stored in encrypted form, it was possible that hackers also obtained the two components needed to descramble the numbers, the company said.

The crisis quickly emerged as one of the largest data breaches on record. By comparison, last year's Equifax hack affected more than 145 million people. A Target breach in 2013 affected more than 41 million payment card accounts and exposed contact information for more than 60 million customers.

Security analysts were alarmed to learn that the breach began in 2014. While such failures often span months, four years is extreme, said Yonatan Striem-Amit, chief technology officer of Cybereason.

The affected hotel brands were operated by Starwood before it was acquired by Marriott in 2016. They include W Hotels, St. Regis, Sheraton, Westin, Element, Aloft, The Luxury Collection, Le Méridien and Four Points. Starwood-branded timeshare properties were also included.

None of the Marriott-branded chains were threatened.

For as many as two-thirds of those affected, the exposed data could include mailing addresses, phone numbers, email addresses and passport numbers. Also included might be dates of birth, gender, reservation dates, arrival and departure times and Starwood Preferred Guest account information.

"We fell short of what our guests deserve and what we expect of ourselves," CEO Arne Sorenson said in a statement. "We are doing everything we can to support our guests, and using lessons learned to be better moving forward."

Marriott set up a website and call center for customers who believe they are at risk.

The stolen information could be used by criminals to create fraudulent bank accounts.

It isn't common for passport numbers to be part of a hack, but it is not unheard of. Hong Kong-based airline Cathay Pacific Airways said in October that 9.4 million passengers' information had been breached, including passport numbers.

Passport numbers are often requested by hotels outside the U.S. because U.S. driver's licenses are not accepted there as identification. The numbers could be added to full sets of data about a person that bad actors sell on the black market, leading to identity theft.

And while the credit card industry can cancel accounts and issue new cards within days, it is a much more difficult process, often steeped in government bureaucracy, to get a new passport.

But one redeeming factor about passports is that they are often required to be seen in person, said Ryan Wilk of NuData Security. "It's a highly secure document with a lot of security features," he said.

Email notifications for those who may have been affected begin rolling out Friday.

When the merger was first announced in 2015, Starwood had 21 million people in its loyalty program. The company manages more than 6,700 properties across the globe, most in North America.

While the first impulse for those potentially affected by the breach could be to check credit cards, security experts say other information in the database could be more damaging.

The names, addresses, passport numbers and other personal information "is of greater concern than the payment info, which was encrypted," analyst Ted Rossman of CreditCards.com said, citing the risk of fraudulent accounts.

An internal security tool signaled a potential breach in early September, but the company was unable to decrypt the information that would define what data had possibly been exposed until last week.

Marriott, based in Bethesda, Maryland, said in a regulatory filing that it was premature to estimate what financial impact the breach will have on the company. It noted that it does have cyber insurance, and is working with its insurance carriers to assess coverage.

Elected officials were quick to call for action.

The New York attorney general opened an investigation. Virginia Sen. Mark Warner, co-founder of the Senate cybersecurity caucus and the top Democrat on the Senate Intelligence Committee, said that the U.S. needs laws that will limit the data companies can collect on its customers.

"It is past time we enact data security laws that ensure companies account for security costs rather than making their consumers shoulder the burden and harms resulting from these lapses," Warner said in a statement.

Marriott has had a rocky process of merging its computer system with Starwood computers. Members of both loyalty programs have complained about missing points, glitches with stays crediting to their accounts and problems with free nights earned from credit cards not appearing.

The company is still trying to phase out Starwood systems, Sorenson said.

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