1. A system for executing a program, the system comprising: a virtual machine monitor which divides an operating system (OS) into at least one root domain and a plurality of domains having different trust levels; a trust-management module which is included in the at least one root domain and which periodically measures and adjusts a trust level of an application program currently being executed in the plurality of domains; and a memory unit storing a component and a processor, wherein the virtual machine monitor executes the application program in one of the plurality of domains in consideration of the measured trust level of the application program, wherein the virtual machine monitor comprises a process-migration-control module that migrates a process of the application program to whichever domain of the plurality of domains is compatible with the trust level of the application program, and the process-migration-control module first freezes a status of the process of the application program, then provides the process of the application program to the domain of the plurality of domains that is compatible with the trust level of the application program, and finally restores the status of the process of the application program.