a. recording on the computer system a dataset for each user to be authenticated to create a user profile for each user to be authenticated, each data set comprising a plurality of free-text keystrokes entered by a respective user on a computer that is part of the computing system, and storing each user profile in the memory;

b. subsequently collecting the keystrokes of a user to be authenticated as the user enters text on a keyboard connected to the computing system;

c. creating a plurality of graphs based on the collection of keystrokes entered by the user in step (b), each of which represents a cumulative density function of the user for each feature shared between the user profile and the user to be authenticated entered in step (b);

d. using the computer, calculating an instance based tail area density (ITAD) metric by:

wherein N is the number of graphs shared between the user profile and collection of keystrokes entered by the user in step (b), CDF_gi(*) is the empirical cumulative distribution function of the i^th graph g_i in the user profile, M_g is the median of the i^th graph in the user profile, X_i is the individual test graph duration for the ith shared graph in the collection of keystrokes entered by the user in step (b);

e. using the computer, combining the ITAD metric for each graph duration into a single similarity score using the following equation:

wherein the parameter p serves as a scaling factor and can be selectively tuned depending on the application, and if 0<p<1, then lower scores are scaled up more than higher scores, and if p>1 then larger scores will be shifted down by a lesser amount than lower scores; and

f. determining, by the computer, whether the user entering the keystrokes in step (b) matches an authenticated user from step (a) based on the single similarity score above a predetermined threshold value.