1. A method for using a user device, comprising: obtaining, during a fingerprint learning phase, a historical portion of user activity data associated with user activity of a user using the user device, wherein the user activity data includes both network traffic data associated with the user device and physical activity data associated with the user device, wherein the network traffic data corresponds to network traffic flows associated with a plurality of users; analyzing, by a computer processor of the user device, the historical portion to generate a fingerprint of the user, wherein the fingerprint represents characteristics of the user activity, wherein the analyzing is performed by a user activity analyzer, the user activity analyzer being configured to perform traffic attribution and block correlation, wherein traffic attribution identifies the user that generated the traffic by comparing user identifiers found in the traffic with the user identifiers (user IDs) that are readily known to be associated to the given user, and wherein block correlation identifies which different user IDs correspond to the same user, wherein generating the fingerprint of the user comprises analyzing the plurality of features to determine a uniqueness measure, the uniqueness measure indicating how specific a feature is to the user, wherein the uniqueness measure is calculated using the following formula: uniqueness=1−((U fx −1)/U all ), where U all represents the number of distinct users identified in the plurality of users and U fx represents the number of users having the feature; obtaining, during a fingerprint matching phase subsequent to the fingerprint learning phase, an ongoing portion of the user activity data associated with the user activity of the user using the user device; analyzing, by the computer processor and based on the fingerprint, the ongoing portion to determine a match, wherein the match is determined at a time point within the fingerprint matching phase; and unlocking, by the computer processor and in response to determining the match, a locked data item for access, the locked data item comprising an authentication credential of the user used to authenticate the user of the device, wherein after determining the match, the authentication credential is automatically accessed by an authentication module to allow the user to access the locked data item, wherein the locked data item is stored on the user device.