Method of protecting a mobile-telephone-type telecommunication terminal

A process for protecting a mobile telecommunication device, the mobile device having a personal software component used to access a communications network, a processing unit, a calculation unit, a secure memory, read-only memory, and at least an operating memory that stores an operating programme and data needed for said programme, said process comprising the following steps:

• a) coding, in the processing unit, the operating programme and data stored in the operating memory of the mobile telecommunication device with a pre-determined key K that is generated using unique information associated with the mobile device stored in the secure memory and unique information associated with and stored in the personal software component, and
• b) enabling a decoding of the operating programme and data with the predetermined key K when:
• the mobile device is started using a start programme stored in secure the read-only memory and,
• the predetermined key K is calculated by the device by accessing the unique information associated with the mobile device stored in the secure memory and accessing the unique information associated with and stored in the personal software component,
• wherein the decoding is performed by the calculation unit on request from the processing unit, the calculation unit which decodes the operating programme and data in blocks and stores the decoded blocks in a register, wherein the processing unit executes functions based on the decoded blocks, and
• wherein said personal software component is a chip card.