Marriott's revelation that as many as 500 million guests may have been affected by a data breach at Starwood hotels, which it bought two years ago, ranks among the largest hacks ever.
It is not clear if some of those included in the final tally are individuals who were counted during every stay.
For comparison, here are some of the worst data breaches in history:
• Yahoo, by far, takes the prize for worst data breach, with a 2013 hack affecting 3 billion accounts.
• EBay asked all of its 145 million active users in 2014 to change their passwords as a precautionary measure because of a hack into personal information. The company was not sure how many people were actually affected by the breach.