Method for loading, installing and executing software items, dubbed loading units, having different levels of trust by a computer processing unit comprising a central processing unit charged with the execution of the instructions of the software items and a secure physical storage area, an operating system being furthermore installed to drive hardware resources of the computer processing unit the method comprising - associating with each loading unit (2, 3, 7) at least one information data structure (11, 12, 13) in respect of the needs and security characteristics of this loading unit; the method being characterized in that it comprises: - associating with the said computer processing unit a dynamic data structure representative of the current security state of the computer processing unit; the said dynamic data structure being updated by way of an autonomous security module after a change of the internal state of the processing unit, the said security module being installed in the secure area; and - validating the needs and security characteristics of each loading unit (2, 3, 7) in respect of the computer processing unit's current state contained in the said dynamic data structure by way of the autonomous security module; and - if the validation is positive, authorizing by the security module the loading, the installation or the execution of the loading unit (2, 3, 7), and in which the said security module, subsequent to the installation of this module, ensures the autonomous control at least of the steps: - of change of internal state of the system; - of demand for access to the resources of the system; - of demand for installation of each loading unit on the system, and in which in addition to the absolute information items and the relative information items, the said security module manages any new event catalogued in the dynamic data structure representative of the current state of the execution system unit, the said security module ensuring the management and the updating of a variable of current level of trust of the system as a function of events that have arisen such as detection of an attack, and the modification of the state of trust after installation or deinstallation of a loading unit. - associating with each loading unit (2, 3, 7) at least one information data structure (11, 12, 13) in respect of the needs and security characteristics of this loading unit; - associating with the said computer processing unit a dynamic data structure representative of the current security state of the computer processing unit; the said dynamic data structure being updated by way of an autonomous security module after a change of the internal state of the processing unit, the said security module being installed in the secure area; and - validating the needs and security characteristics of each loading unit (2, 3, 7) in respect of the computer processing unit's current state contained in the said dynamic data structure by way of the autonomous security module; and - if the validation is positive, authorizing by the security module the loading, the installation or the execution of the loading unit (2, 3, 7), - of change of internal state of the system; - of demand for access to the resources of the system; - of demand for installation of each loading unit on the system,