If you stayed at a Hilton, Marriott, Sheraton, or Westin hotel last year, check your credit card and bank statements.
A spokesman for the company that runs these hotels says hackers got through security.
Hundreds of customers may have had their information stolen.
Bankers have already seen some of the card numbers used by the hackers.
White Lodging is the company that runs the hotel chains.
Investigators are working with the company to find the hackers.