One good habit to form when using the ATM is to always cover you hand when entering your PIN, because unless you're an expert at detecting card skimmers, you'll likely never know when you're being watched. The above device was discovered at a bank in California's San Fernando Valley earlier this year. Aside from a tiny pinhole to the right of the card slot (which houses a camera), it's nearly impossible for an average citizen to distinguish this device from a real ATM.
Police believe that there are more ATM skimmers out there, and while this specific one was located in California, you should always exercise extreme caution when using ATMs. The devices are capable of recording all of your card details, so when coupled with your PIN, the thieves can do some serious damage to your bank account. This isn't John Connor hacking into an ATM with an Atari Portfolio, these are serious professionals who know what they're doing.