4. Marriott says 500 million guests could be affected by Starwood data breach

Up to 500 million guests who made reservations at Starwood properties around the world since 2014 may have had their personal information compromised after a data breach by "an unauthorized party" targeted its guest reservation system, Marriott announced on Friday, per the Wall Street Journal.

Details: The compromised information includes "names, addresses, phone numbers, email addresses, passport numbers, and travel details" for two-thirds of those affected, according to the WSJ. And Marriott couldn't definitively state that card payment information hadn't been stolen as well, though it noted that information is usually encrypted.