Alphanumeric describes a string of characters made of letters (A–Z) and digits (0–9), sometimes with a few symbols allowed. Much of finance runs on alphanumeric identifiers. A SWIFT code mixes bank, country and location letters with numbers, and an IBAN starts with a two-letter country code followed by check digits and an account number. In crypto, a wallet address is a long alphanumeric string derived from a public key, and some formats leave out look-alike characters such as 0, O, I and l to cut copying errors. Because these strings are hard to read, people often check only the first and last few characters, which scammers exploit in address poisoning. Strong passwords are alphanumeric too.