In today's rapidly changing globalized world, remarkably fast and important developments have been faced in the area of national security as in almost all other areas. Advancements in communication and transportation technologies have removed physical boundaries almost completely. National security institutions now have to fight against new and complicated security threats that go beyond the boundaries such as organized crimes and terror crimes. These ever-changing threats and dangerous environment which become more and more complex every single day force nations to review their current security structures and to take new and effective measures in the required areas in order to ensure their national security. As a matter of fact, counter-intelligence, which was quite important due to the frequency of spying acts during the Cold War but lost its importance after the Cold War had ended, has been one of these measures. Today, counterintelligence has once again become one of the most important functions in the fight against national security threats with changing dimensions. It is only possible for a nation to ensure its national security fully by having not only a defensive and passive approach but also offensive counter-intelligence.