A security and protection device (1) for protection of the data and executable codes of any fixed or portable computer system and that has a memory medium to be protected. The security and protection device (1) is located physically between the computer system (2) and the memory medium (MP) to be protected, in order to allow the computer system (2) access to the data and codes to be protected after execution of the protection functions independently of the machine code executed by the computer system (2) and requires no interaction with the processor of the system for the execution of these functions.