DEFINITION of 'Message Authentication Code - MAC'
A security code that is typed in by the user of a computer to access accounts or portals. This code is attached to the message or request sent by the user. Message authentication codes (MACs) attached to the message must be recognized by the receiving system in order to grant the user access. MACs are commonly used in electronic funds transfers (EFTs) to maintain information integrity.
BREAKING DOWN 'Message Authentication Code - MAC'
Message authentication codes are usually required to access any kind of financial account. Banks, brokerage firms, trust companies and any other deposit, investment or insurance company that offers online access can employ these codes.