ATM skimmers, the miniature devices that stealthily help fraudsters capture your credit and debit card data, are getting smaller and harder to detect. Skimmers have always been designed to blend in with any ATM they're attached to, but for years a discerning eye or tug of the card reader were often enough to uncover them. That's not the case anymore. Krebs on Security has been researching a number of devices recovered in Europe this year, and several of them were small enough to fit inside the ATM card slot itself. The ultra-thin profile of these "insert skimmers" makes them far less obvious to your average person making a quick stop at the cash machine.

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This translucent card skimmer sits right inside the card slot of an ATM machine. (Krebs on Security)

And thieves often pair them with hidden spy cameras that are equally difficult to spot; many victims never realize their banking data has been compromised until fraudulent charges begin showing up. Other modern skimmers include mobile chips capable of sending off your credit card data in a text message, so the perpetrator can avoid the risk of returning to the host ATM and picking up the device.

The United States and its snail-like pace to adopting chip and PIN debit / credit cards can be blamed for the growing skimmer problem. Until the US is fully on board, international banks have little choice but to keep manufacturing cards with the vulnerable magnetic stripe. For now, the best protection is covering an ATM's keypad when entering your PIN — and keeping your eyes open for card slots that show signs of tampering.