Every time you enter your credit card number into a form the credit card processor will perform a series of security checks based on the information that those numbers give away.
Credit card numbers are not randomly assigned, each digit in the number sequence has a meaning. Some companies like department stores and phone companies have their own numbering systems, but ANSI Standard X4.13-1983 is the system used by most national credit card systems.
Credit card number length will change depending from issuer, the most usual is 16 digits divided in groups of 4.
Credit card number length
The first credit card number will always be 3, 4, 5 or 6 and it is known as the Major Industry Identifier (MII), this number represents the entity which issued your card.
American Express: 15 digits
Visa: 13 or 16 digits
Mastercard: 16 digits
Discover: 16 digits
Diner’s Club/Carte Blanche: 14 digits
Meaning of the credit card first digit
American Express and Diners Club credit cards also use a second digit to identify the company. Diners Club cards will start with either 36 or 38, and American Express cards use 34 or 37.
The rest of the credit card digits meaning will vary depending on credit card type and issuing company. Normally the numbers grouped after the opening series are the routing number of the bank and the next group of digits represents the user’s account number.
Number 3: Travel and entertainment cards such as American Express or Diners Club.
Number 4: Visa credit card and Visa branded debit cards.
Number 5: Mastercard credit card and Mastercard branded debit cards.
Number 6: Discover credit card.
The other credit card numbers explained
American Express: Digits three and four are type and currency, digits from five to eleven are the account number, digits from twelve up to fourteen are the card number within the account and digit fifteen is the check digit.
Visa: Digits from two through six are the bank number, digits seven through twelve or seven through fifteen are the account number and digit thirteen or sixteen (depending on credit card numbers length) is the check digit.
MasterCard: Digits two and three, two through four, two through five or two through six are the bank number (depending on whether digit two is a 1, 2, 3 or other). The digits after the bank number up through digit fifteen are the account number, and digit sixteen is a check digit.
The final credit card number is a check digit, a checksum number calculated using the Luhn algorithm and used for fraud check purposes.
Credit and debit card security code explained
Credit and debit cards also contain a credit card verification code that it is known as CCV, CSC,CVC2, CVV2, CID2 and many other acronyms depending on who the credit card issuer is.
MasterCard, Visa, Diners Club, Discover, and JCB credit and debit cards have a three digit card security code printed at the back of the card but the latest US MasterCard and Visa cards feature this code in a separate panel to the right of the signature strip to prevent overwriting of the numbers when you sign the card.
American Express cards have a four-digit code printed on the front side of the card above the number and they call it Card Identification Number ( CID).
The credit card verification value is normally used for card not present transactions, like shopping over the Internet or buying items by mail, credit card regulations state that this number can never by stored by the merchant making it more difficult for a thief to get hold of it.
The card verification value at is calculated by encrypting the bank card number, expiration date and service code using encryption keys known only to the issuing bank, the end result is the three of four digit decimal number printed on your card.