1. A computer-implemented method for unlocking functionality of a mobile device, comprising: under the control of one or more computer systems with executable instructions, obtaining information corresponding to interactions with applications executed on a mobile device, the applications lacking privileges to set unlock settings of the mobile device; generating a set of security tasks based at least in part on the interactions; detecting a trigger for displaying a user interface for unlocking the mobile device; selecting a security task from the set of security tasks; displaying the selected security task through the user interface, where the user interface requires a response to the security tasks before enabling use of the mobile device; receiving a response to the displayed security task; calculating a confidence score based at least in part on the response; determining, based at least in part on the calculated confidence score, to require a next response to the next security tasks prior to enabling use of the mobile device; displaying the next security task through the user interface; and unlocking the mobile device as a result of determining the next security task was completed successfully.