Credit Cards Codes and Numbers
Credit card codes and numbers are one of the security mechanisms, aimed reducing credit card fraud. Credit cards are often criticized for their low security, which opens the door to various kinds of fraud but even when security is low, it is better than nothing. In that respect, credit cards numbers and codes are simply one more attempt to make the illegitimate use of credit cards a difficult task. If this attempt is a successful one or not, is a different topic.
Probably you have seen the numbers on the front and on the back of your card. They might look like random numbers but actually they have their internal logic. The rules regarding their numbering scheme are regulated on a global scale and every credit card issuer has to conform to them. However, since the rules are pretty loose, not all credit cards have all the same attributes. But the good news is that many of the attributes are mandatory, so they are present on every single card issued somewhere in the world.
For instance, each card has a number. Usually credit card numbers are 15 or even more digits long, so that the chance to guess somebody else's credit card number accidentally is incredibly small. The first digit of the credit card number is the Major Industry Identifier (MII) and it shows what kind of institution (airlines, banks, travel companies, etc.) your card has been issued by. If the last digit is 9, then national rules about further assignment apply.
The next five digits after the MII digit identify the issuer. Usually these five digits are grouped with the first digit, so actually there are more than a million possible combinations for issuers. Generally big issuers like Diner's Club, American Express, VISA and MasterCard have a range of digits assigned to them (for instance for American Express this range is 34xxxx and 37xxxx), which allows to identify not only the master company but also which of its branches issued the card.
The six digit codes apply mostly for American issuers. For international issuers, the next 3 digits after the MII are the 3-digit country codes as defined in ISO 3166 and only the last two digits are actually used for issuer identification, mainly on a national level.
The digits from the seventh digit to the digit before the last one are the account number - i.e. if your credit card number has 19 digits, which is the maximum possible length, then the numbers from 7 to 18 are your account number. The very last digit is a control digit, so the maximum length of a credit card account is 12 digits, although most often it is much shorter than that.
The last digit is the check digit. Its value is calculated with the help of a complex algorithm (the Luhn algorithm) and getting into much detail about it is outside the scope of this article. What is important to know is that if the last digit does not match the result of the number-crunching per the Luhn formula, then your card number is simply invalid. It is the last digit in the credit card number that helps make the initial verification if a card number is valid or not. Since banks issue valid numbers only, then if somebody tries to buy goods from you with an invalid card number, then he or she is trying to cheat you.
The check digit in a credit card number is not the only security mechanism modern credit cards have. In addition to it, there is one more code – Card Security Code or Card Verification Code – which is also used to check if the card is valid. This code has two varieties – CVC1 or CVV1 and CVC2 or CVV2. The first one is used for face-to-face purchases (i.e. in a shop) and the second is for online purchasing (i.e. in cases where the card is not physically available). The first one is encoded in the magnetic stripe of the card and is read by card readers and the second one is cited by you to verify that the credit card is a valid one. However, the security provided by CVC2 or CVV2 is pretty fake because once a phisher learns your code, he or she can make all kinds of purchases with your credit card.