I definitely agree that the Russian Orthodox Church was highly infiltrated by the KGB during the Soviet Union. I have a sense that it is less so today by the KGB’s successor. There was a great underground Christian ‘movement’ during the Soviet years. The KGB managed to infiltrate the ROC, but they did NOT destroy Christianity in the USSR.
I used to know a Russian guy whose family had an icon. During the communist years, it hung on the back of the front door. That way, if communist inspectors or police or whatever came to visit, it was concealed as long as the door remained open.
Also, icons over the years can go completely black with smoke from candles burning in front of them. During communism, many people took advantage of this fact. The family that owned it knew it was an icon, but the authorities couldn’t tell by looking at it.