Android’s intent framework serves as the primary method for interprocess communication (IPC) among apps. The increased volume of intent IPC present in Android devices, coupled with intent’s ability to implicitly find valid receivers for IPC, bring about new security challenges. We propose Intentio Ex Machina (IEM), an access control solution for Android intent security. IEM separates the logic for performing access control from the point of interception by placing an interface in the Android framework. This allows the access control logic to be placed inside a normal application and reached via the interface. The app, called a “user firewall”, can then receive intents as they enter the system and inspect them. Not only can the user firewall allow or block intents, but it can even modify them to a controlled extent. Since it runs as a user application, developers are able to create user firewalls that manufacturers can then integrate into their devices. In this way, IEM allows for a new genre of security application for Android systems offering a creative and interactive approach to active IPC defense.