Moving-target defense is an effective strategy for deflecting cyber attacks. The widespread use of smartphones in the tactical field requires novel ways of securing smartphones against an ever-increasing number of zero-day attacks. We propose a new, proactive approach for securing smartphone apps against certain classes of attacks. We leverage smartphone's native support for quick and lossless restarts to make application restart a cyber maneuver meant to deflect and confuse attackers. We propose a time-series entropy metric to quantify attack resilience. We apply our approach to 12 popular Android apps chosen from a variety of domains, including online banking and shopping. Preliminary experiments with using proactive restarts on these apps show that restart is a promising way of increasing attack resilience for a certain class of side-channel attacks named Activity Inference attacks.