How they work: Credit Cards are issued to users after an account has been approved by the credit card provider, with which he or she will be able to make purchases from merchants accepting that credit card up to a pre established credit card limit. When a purchase is made, the owner of the credit cards agrees in advance to pay the card issuer. Originally the user would indicate his/her consent to pay, by signing a receipt with a record of the card details and indicating the amount to be paid, but many merchants now accept verbal authorizations via telephone and electronic authorization using the Internet. Credit cards are a type of retail purchasing settlement and credit system, so called because of the small plastic credit card issued to users. Credit cards are different from a debit cards due to the fact that the credit card issuer lends the consumer money rather than having the money removed from an account. It is also different from a charge card (though this name is sometimes used by the public to describe credit cards) in that charge cards require that the balance must be paid in full at the end of the month. In contrast, a credit card allows the consumer to 'revolve' their balance, at the cost of having interest charged. Most credit cards are similar in shape and size, as specified by the ISO 7810 standard

For example, a website that uses SSL to encrypt card numbers from a client may simply email the number from the webserver to someone who manually processes the card details at a card terminal. Naturally, anywhere card details become human-readable before being processed at the acquiring bank is a security risk. However, many banks offer systems such as ClearCommerce, where encrypted card details captured on a merchant's webserver can be sent directly to the payment processor.