From your linked page: Most small online businesses do not store credit card data locally, but that doesn't stop you from using salted hashes of credit card nu

From your linked page: Most small online businesses do not store credit card data locally, but that doesn't stop you from using salted hashes of credit card numbers to compare. Storing a "salted hash" of a credit card number in the manner you describe is only fractionally better than storing the credit card number itself. This is because credit card numbers have very little entropy - less than 36 bits per issuer code, so bruteforcing these hashes can be done very quickly.