The document discusses implementing security on Android applications. It provides an overview of the Android architecture, including its application model and security mechanisms like isolation, permissions, and signatures. It then reviews the Android software stack and key components like the activity manager, notification manager, and package manager. Next, it describes a system called TISSA that aims to provide security for user contacts, call logs, and location data by regulating access through a privacy settings content provider and privacy aware components. However, it notes that TISSA has limitations like occasionally providing fake responses and only using single privacy settings per private information type.