A computer to boot from a user trusted device, the user trusted device comprising a connection interface enabling connection with said computer, the method comprising: enabling said computer to start booting from the user trusted device upon connection of the user trusted device with said computer via said connection interface; instructing a processor of the computer to execute virtualization sensitive code and issue completion data upon completion of execution, which completion data depends on the virtualization sensitive code and its execution by the processor; determining, based on said completion data, whether the execution was not performed in a virtualized environment; and enabling said computer to complete booting from the user trusted device upon determining that the execution was not performed in a virtualized environment. The invention is further directed to a user trusted device enabling this method and to related systems.