Most credit-card and debit-card numbers are a sequence of 16 digits, with the final number in the sequence being a “checksum,” or a calculated number that was once useful in checking that a card number provided was legitimate. Card numbers can easily be stolen in a lot of ways, including thieves obtaining lists of numbers that were issued through people working in the industry, subverting databases, or even hijacking websites and intercepting data. One technique to reduce the misuse
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