A mobile device and a method of operating a mobile device are disclosed. The mobile device includes a main processor executing a normal code of a mobile application program, a co-processor executing a core code of the mobile application program, and a co-processor driver enabling the main processor and the co-processor to communicate with each other. The normal code includes commands executable by the main processor, and the core code includes commands executable by the co-processor. Since the core code is separated from the mobile application program on a level lower than an operating system level when the mobile application program is installed on the mobile device and the core code is stored in a core code storage to which the main processor is not allowed to access directly, the core code is not exposed to an attacker, such that resistance to a reverse engineering attack is increased.