The mobile cloud is the integration of smart sensors, mobile devices, and cloud computers in a well-connected ecosystem. Such integration can improve the efficiency of services. However, such integration also leads to security and trust issues. For example, the security of cloud spaces has sometimes been breached through accessing of peripheral devices, such as HVAC system. This chapter will show how mobile cloud security and trust can be improved while maintaining the benefits of efficiency by supporting fine-grained mobility. Specifically, we discuss an actor-based programming framework that can facilitate the development of mobile cloud systems in a way that improves efficiency while enforcing security and privacy. There are two key ideas here. First, by supporting fine-grained units of computation (actors), a mobile cloud can be agile in migrating components. It does so in response to a system context (including dynamic variables such as available bandwidth, processing power, and energy) while respecting constraints on information containment boundaries. Second, by specifying constraints on interaction patterns, information flow between actors can be observed and suspicious activity flagged or prevented. We introduce the concepts and discuss their realization in notations and prototypes. Finally, we will discuss open research issues such as inference of interaction patterns.