A digital system is provided with a secure mode (3rd level of privilege) built in a non-invasive way on a processor system that includes a processor core, instruction and data caches, a write buffer and a memory management unit. A secure execution mode is thus provided on a platform where the only trusted software is the code stored in ROM. In particular the OS is not trusted, all native applications are not trusted. The secure mode is entered through a unique entry point. The secure execution mode can be dynamically entered and exited with full hardware assessment of the entry/exit conditions. A secure mode indicator is provided to tell a user of the digital system that the device is in secure mode. This indicator may be a small LED, for example. The user should not enter any secret information (password) or should not sign anything displayed on the screen if the secure mode indicator is not active.