Point of Sale Systems Pose a Threat
Hackers have been exploiting point of sale systems that store credit card data and also are connected to the Internet. this is done by guessing the password that is used for remote administration of the system or else exploiting known bugs in the particular system.
A recent casualty is Destination Hotels & Resorts, a high-end chain best known for its resort hotels in destinations such as Vail, Colorado; Lake Tahoe, California; and Maui, Hawaii. Hackers may have stolen the credit card numbers of guests who have stayed there. How many is anybody's guess, apparently. Similar episodes have occurred at Wyndhams, another big hotel chain. For a report on the latest, see this link.
It points to the need for good security over such systems, including strong access control over admin accounts and staying on top of system bugs and the related vulnerabilities.