1. A method performed by a hardware processor for authenticating an unknown user claiming to be a legitimate user, the method comprising: presenting, by the hardware processor, to the unknown user a plurality of prime images, wherein the plurality of prime images are presented to the unknown user in an amount of time that is less than or equal to 16 milliseconds such that the plurality of prime images are consciously unperceivable and subconsciously perceivable by the unknown user to induce one or more conditioned responses; observing, by the hardware processor, one or more responses, by the unknown user, to the plurality of prime images that are consciously unperceivable and subconsciously perceivable by the unknown user; generating, by the hardware processor, an unknown user response metric based on the observed one or more responses; comparing, by the hardware processor, a known conditioned user response metric to the unknown user response metric; one of preventing access to a computer system and decreasing a level of access to the computer system when the unknown user response metric differs from the conditioned user response metric by more than a predefined degree of acceptable variation, wherein the conditioned user response metric represents observed changes in micro-behaviors of the legitimate user in response to viewing the plurality of prime images, and the unknown user response metric represents observed changes in micro-behaviors of the unknown user in response to viewing the plurality of prime images; and one of granting access to the computer system and maintaining the level of access to the computer system when the unknown user response metric matches the legitimate user response metric by less than the predefined degree of acceptable variation.