“Consider spoofing. In the strategic confrontation between the United States and the Soviet Union, the adequacy of air defences was a vital issue. It was item (3) on General Cabell’s list. If you could find a weakness, it might be the key to ‘victory’ in an all-out nuclear war. The only sure way to test your adversary’s defences is to fly an aircraft over their borders and see how long it takes for them to notice. The United States did this routinely to test Soviet air defences. In the 1950s and 1960s, the United States had state-of-the-art radar defense systems covering its west and east coasts, and especially its northern approaches (over which a Soviet bomber or missile attack would most likely come).”
I have no idea what "spoofing’ means, please help me.