Most major credit cards share a similar numbering scheme. The first few numbers in the overall sequence are called the "prefix," and are used to note the card's distributor. For example, American Express credit card numbers usually begin with 34 or 37, Visa numbers usually start with 4, and so on.

The first six digits of a credit card number identify the institution that issued the card. This is known as the Bank Identification Number (BIN). This also notes the network that the card is connected to.

Fake Credit Card Numbers

Credit card number generators are software devices that can be used to fabricate fake credit card numbers. These programs use a special algorithm to calculate possible credit card numbers, with the intention of replicating an existing account number.

Although most of the numbers that the programs produce are worthless, they do occasionally provide a cyber-criminal with a valid account number. These numbers are then used to steal goods and services online. Sites that don't verify the identity of the cardholder making a purchase are especially vulnerable to these bogus credit card numbers.

Many credit card companies secure their numbers by using what is known as a "checksum" test. This is a simple process for ensuring data integrity, where the final number of the sequence is used to confirm the rest of the numbers. This not only protects the account from random attempts to create a valid number, but also from clerical errors where the wrong digits might be manually recorded.