Personal mobile devices like smartphones and tablets are ubiquitous. People use mobile devices for fun, for work, and for organizing and managing their lives, including their finances. This has become possible because over the past two decades, mobile phones evolved from closed platforms intended for voice calls and messaging to open platforms whose functionality can be extended in myriad ways by third party developers. Such wide-ranging scope of use also means widely different security and privacy requirements for those uses. As mobile platforms gradually opened, platform security mechanisms...