16. The method of claim 14 wherein repeated questioning of the user on such personal questions is effected to attempt to promote the confidence level of access authorization.
14. A user authentication method for use in controlling access to a computer system having a keyboard, that comprises, inputting at such keyboard the owner's log-in name and password; extracting the owner's timing vectors from keyboard stroke characteristics with which the owner repeatedly has typed the owner's password to form a training set; setting up a semantic network using multiple links to indicate that different pattern components of a user's behavioral access create different kinds of symbolic representations rather than just simple connections or links; setting up neural network training by using each of the owner's timing vectors in the training set as input thereto; thereafter when a user inputs the owner's log-in name and password, checking if the user's password is identical to the owner's password; extracting the user's timing vector from a keystroke characteristic to type the user's password if the checked result is affirmative; otherwise, demoting the user in confidence level for accessing the system; applying the user's timing vector to the trained neural network as in input; comparing the difference between such input and an output of the neural network with a predetermined threshold; and permitting user access to the system if the difference is not greater than such threshold, while demoting the confidence level or prohibiting access to the system, if otherwise; and monitoring the user's response time to commence answering questions personal to the owner to adjust the setting of the confidence level.