BIN (Bank Identification Number)

The Bank Identification Number (BIN), also called the Issuer Identification Number (IIN), is the leading digits of a credit, debit, or prepaid card number. They encode the card network (Visa, Mastercard, etc.), the issuing bank, the card type (credit/debit/prepaid), and sometimes the country of issue.

Fraudsters use BIN data in two main ways. First, in BIN attacks (also called BIN enumeration), they test thousands of generated card numbers that share a known BIN, submitting small authorisation requests to identify valid full card numbers. Second, BIN lookups help criminals purchase targeted card details on dark web marketplaces — knowing a card's BIN tells them the issuing bank, which may have weaker fraud controls.

Merchants and fraud prevention systems use BIN data to flag suspicious orders — for example, when a billing address is in one country but the BIN indicates a card issued in a different country.