What is an ATM Skimmer?

ATM "Skimming" is the criminal practice of obtaining debit card numbers and their corresponding PIN numbers, and using this information to steal money from bank customers' accounts. A skimmer can obtain your PIN number simply by watching over your shoulder as you use an ATM machine. Others use high-tech equipment, so they don't even have to be anywhere near the victim. A second card reader is placed over the real slot on an ATM, and a tiny camera is placed somewhere along the side of the ATM. The camera records the PIN number as the customer presses the keypad, and can even record the entire transaction as displayed on the ATM's monitor. The camera and card reader broadcast the data to the criminals who are parked several feet away. They use the information to create counterfeit cards and withdraw money from the victims' accounts.

Source:
Mikkelson, Barbara & David P. ATM Camera. Urban Legends Reference Pages (Snopes.com). 1 February, 2010. Web. Accessed 19 July, 2010.
<http://www.snopes.com/fraud/atm/atmcamera.asp>