What is the chance someone could randomly place down numbers and....?

Question

get somebodies credit card number? Just thought of it, no reason lol

Answer 1

they could possibly get credit cards number by a this method but they are useless these days as to have a successful credit card manual transaction these days you need the expiry date and cvc code to get a successful transaction

Answer 2

It's very, very improbable.  But here's a breakdown to help you understand just what all the numbers do in fact mean.

The first digit of your credit card number is the Major Industry Identifier (MII), which represents the category of entity which issued your credit card. Different MII digits represent the following issuer categories.

The first 6 digits of your credit card number (including the initial MII digit) form the issuer identifier. This means that the total number of possible issuers is a million (10 raised to the sixth power, or 1,000,000).

If the MII digit is 9, then the next three digits of the issuer identifier are the 3-digit country codes defined in ISO 3166, and the remaining final two digits of the issuer identifier can be defined by the national standards body of the specified country in whatever way it wishes.

Digits 7 to (n - 1) of your credit card number are your individual account identifier. The maximum length of a credit card number is 19 digits. Since the initial 6 digits of a credit card number are the issuer identifier, and the final digit is the check digit, this means that the maximum length of the account number field is 19 - 7, or 12 digits. Each issuer therefore has a trillion (10 raised to the 12th power, or 1,000,000,000,000) possible account numbers.

The final digit of your credit card number is a check digit, akin to a checksum. The algorithm used to arrive at the proper check digit is called the Luhn algorithm, after IBM scientist Hans Peter Luhn (1896-1964), who was awarded US Patent 2950048 ("Computer for Verifying Numbers") for the technique in 1960.

Now, the most common credit cards have 16 digits, so there are 10^16 different combinations possible.  That's 10,000,000,000,000,000.  I don't know how many cards are in existence, but if you plunk down numbers entirely at random you'll only pass the validation number once in ten.  So the first number can be anything.  Doesn't matter.  But it then has to correspond to the next five numbers as an issuer, of which there can be a million.  Then your account number has to actually exist, plus the check number has to pass muster.  I can't tell you the actual probability because I don't know how many credit cards exist.  But it is vanishingly small.  Each issuer has a trillion numbers to work with.  And there can be a million issuers.  Plus a one in ten check number.  Let's say everybody on Earth has six credit cards, for a total of about 36 billion.  You'd still only have a 0.00000036% chance of getting a real number by guessing at random.