The invention concerns a process to protect a vulnerable software working on a data processing system against its unauthorized usage using a processing and memorizing unit. The process comprises defining: 1) a set of dependent functions whose dependent functions are liable to be executed in a processing and memorizing unit 2) a set of triggering commands, said triggering commands being liable to be executed in the data processing system and to trigger the execution in a processing and memorizing unit, of the dependent functions 3) for each triggering command, an order 4) a method of renaming of the orders 5) restoring means designed to be implemented in a processing and memorizing unit during a usage phase, and enabling to restore the dependent function to execute, from the renamed order.