18. The system of claim 12 , wherein the recent contextual data of the user comprise one or more of: GPS data, accelerometer data, voice data, sensor data, application usage data, web browser data, authentication attempts, connection attempts, network traffic patterns, DNS requests, typing patterns, biometric data, social group membership information, and user demographics data.
12. A system for implicitly authenticating a user to access a controlled resource, the system comprising: a user access request receiver configured to receive a request, from a computer device, to access the controlled resource; a selection mechanism configured to select a user behavior model for the user, wherein the user behavior model is derived from historical context data of the user; a determination mechanism configured to determine recent contextual data of the user, wherein the recent contextual data are collected from one or more user devices without prompting the user to perform an action associated with authentication, and wherein the recent contextual data comprise a plurality of data streams which provide a basis for determining whether the user owns the computing device; a behavioral score grader configured to determine a user behavior score which indicates a likelihood that the user owns the computing device, wherein while determining the user behavior score the behavioral score grader is further configured to: observe a recent event that is associated with the user's computing device; calculate a quality measure for the recent event, and a weight associated with a type of the observation; determine that the observed recent event is consistent with the user behavior model; and adjust the user behavior score based on the quality measure and the weight; and an authentication information provision mechanism configured to provide the user behavior score to an access controller of the controlled resource, wherein the access controller is configured to facilitate access to the controlled resource for the user in response to the user behavior score exceeding a predetermined threshold value.