Skimming

Skimming is the theft of credit card information used in an otherwise legitimate transaction. It is typically an "inside job" by a dishonest employee of a legitimate merchant, and can be as simple as photocopying of receipts. Common scenarios for skimming are restaurants or bars where the skimmer has possession of the victim's credit card out of their immediate view. The skimmer will typically use a small keypad to unobtrusively transcribe the 3 or 4 digit Card Security Code which is not present on the magnetic strip. Many instances of skimming have been reported where the perpetrator has put a device over the card slot of a public cash machine (Automated teller machine), which reads the magnetic strip as the user unknowingly passes their card through it. These devices are often used in conjunction with a pinhole camera to read the user's PIN at the same time.^[2]

Skimming is difficult for the typical card holder to detect, but given a large enough sample, it is fairly easy for the bank to detect. The bank collects a list of all the card holders who have complained about fraudulent transactions, and then uses data mining to discover relationships among the card holders and the merchants they use. For example, if many of the customers used one particular merchant, that merchant's terminals (devices used to authorize transactions) can be directly investigated. Sophisticated algorithms can also search for known patterns of fraud. Merchants must ensure the physical security of their terminals, and penalties for merchants can be severe in cases of compromise, ranging from large fines to complete exclusion from the merchant banking system, which can be a death blow to businesses such as restaurants which rely on credit card processing.