This information is acquired with a 'skimmer'. A basic skimmer consists of a magnetic card reader head and an electronic circuit that either stores or transmits the data that is read by the magnetic card reader head. Typically, the skimmer is built into a fake card reader, which is then placed over a real card reader. Other varieties include a complete false ATM face that covers the entire front of the machine and includes a skimmer card reader, or skimmers that are placed just before or after the slot of a 'swipe'-type card reader, so that its magnetic head reads the card strip when the card is swiped. The latter type of card readers are often found in indoor cash register PIN pads in stores, or entry door access systems such as a vestibule door that gives access to an indoor bank ATM.
The skimmer is quickly attached by the criminal, who is making sure that the skimmer optically blends in with the rest of the machine that the skimmer is placed on, in order to avoid any suspicion. The card information that is skimmed is then either wirelessly transmitted by the skimmer, or simply stored in an electronic memory chip inside the skimmer. In case memory storage is used, the criminal has to return to the skimming location to retrieve the skimmer so that its stored account information can be read.