One thing that characterized the Cold War is the intensive use of intelligence agencies to gather information from the other side. US and Soviet forces not only used their own intelligence units, but got help from their allies as well.
Thus, it is unsurprising to find out that counterintelligence also played a vital role. Counterintelligence, as you might have guessed it, is the art and science of blocking intrusion attempts from the enemy.
Link: A Historical Dictionary of Cold War Counterintelligenc
