The information of as many as 500 million people staying at Starwood hotels has been compromised and Marriott says it's uncovered unauthorized access that's been taking place within its Starwood network since 2014.

The company said Friday that credit card numbers and expirations dates of some guests may have been taken.

Marriott said that there was a breach of its database in September, which had guest information related to reservations at Starwood properties on or before Sept. 10.

Marriott discovered through the investigation that someone copied and encrypted guest information, and says it's now working toward removing the information.

Marriott has set up a website and call center for anyone who thinks that they are at risk, and on Friday will begin sending emails to those affected.