ATM skimming is like identity theft for debit cards: Thieves use hidden electronics to steal the personal information stored on your card and record your PIN number to access all that hard-earned cash in your account. That's why skimming takes two separate components to work. The first part is the skimmer itself, a card reader placed over the ATM's real card slot [source: Krebs]. When you slide your card into the ATM, you're unwittingly sliding it through the counterfeit reader, which scans and stores all the information on the magnetic strip.