Would You Have Spotted the Fraud? — Krebs on Security

Card skimmers, in some respects, are rather impressive devices.  Designed to be invisible, they can be installed by criminals on ATMs, gas pumps, or essentially anything else with a card slot.  The principle is easy…your card gets scanned when you insert it into the machine and generally a camera will be located nearby to record your PIN when you type it in.  With this information, a criminal is able to simply reproduce your card for his or her own use.

As far as I know I’ve never actually seen one.  Just be safe and be observant…if a machine doesn’t look quite right then go somewhere else.

Source: Would You Have Spotted the Fraud? — Krebs on Security.