A method of identifying a user as an authorized user from free test text typed by that user into an input device. From the received test text, features associated with the typed text are extracted, such as timing data associated with alphanumeric letter pairs. These extracted features are compared to previously stored series of authorized user profiles, where the authorized user profiles were generated from a trial typing sample of alphanumeric data from each associated authorized user. The comparison identifies one of the authorized users with the user, and a score is derived to measure the strength of the comparison. If the score exceeds a threshold level, the user is identified as that authorized user.