III. SECURITY MODELS:
A. iOS: The iOS is considered as one of the most secured OSs for smartphones. It has a strict control over its different components: hardware, OS, and applications [3]. The Apple's designers enhanced their model to reach to a model which can dispense any third party antivirus [4]. Two different views of iOS security model are presented. The first model stands on four pillars that are mentioned in [4] and are as follows: