OK. I was an air traffic controller for 20 years, that is how I know about squawks. Nothing struck fear into our hearts, more, than the possibility of seeing a 7500 squawk. On 9/11, the chumps turned off the squawkers, so they could not be followed very closely. I worked in radar and I can assure you, it was almost impossible to watch aircraft, when their transponders were turned off. Later bro.
I remember I rented a plane a few days after 9/11 (airspace in Canada opened a couple of days before the US) and posted at the FBO was the starkest memo I’d ever seen. It was from the US government stating that any aircraft crossing the border would be fired upon without warning.