A method performed by an embedded system controlled by a CPU and capable of operating as a virtualized system under supervision of a hypervisor or as a non-virtualized system under supervision of an operating system, is provided. The embedded system is executed in a normal mode if no execution of any security critical function is required by the embedded system, where the normal mode execution is performed under supervision of the operating system. If a security critical function execution is required by the embedded system, where protected mode execution is performed under supervision of the hypervisor, the operating system is switching execution of the embedded system from normal mode to protected mode, by handing over the execution of the embedded system from the operating system to the hypervisor, and when execution of the security critical function is no longer required by the embedded system is switched from protected mode to normal mode, under supervision of the hypervisor.