I remember this discussion going as far back as the 1970’s at least where computers can “broadcast” data through its bus via the RFI (Radio Frequency Interference) they put out. I think back in the 1950’s, someone did something similar where they were able to program the computer to “play music” on a nearby transistor radio by manipulating the RFI it puts out. They did something similar in the 1970’s I think either using an old TRS-80 or an Altair 8800.
Military COMSEC (Communications Security) briefings in the 1970s typically cited how Soviet ELINT (Electronics Intelligence) fishing trawlers operating off American coasts, such as an office in Washington D.C., intercepted RFI (Radio Frequency Interference) emissions from Teletype KSR (Keyboard Send/Receive) printers and computer CRT (Cathode Ray Tube) monitors and used it to reproduce the characters displayed on the devices. The response was to use TEMPEST rated equipment to secure such communications. It was also stressed that there was no such thing as a private or secure telephone call. During Second World War the German intelligence services broke the Allied secure telephone systems to listen in on the conversations between President Roosevelt and Prime Minister Churchill.