A serial number is a unique identifier assigned to a device by its maker or assembler. It is commonly used for inventory, warranty support, repairs, licensing, and traceability. Unlike a password or cryptographic key, a serial number is usually meant to be visible and shareable, not secret.
In cyber security, that distinction matters because systems sometimes rely on a serial number as part of access control or device validation. If a product treats the number as proof of identity, an attacker may be able to copy, spoof, or replay it and convince the system that an unauthorized device is legitimate. Defenders reduce this risk by pairing serial numbers with stronger checks such as signatures, challenge-response protocols, secure hardware identities, or server-side enrollment records. In short, a serial number is useful for identification, but it should not be the only thing standing between a device and trust.