I mean the Voyager 1 probe which is currently the human-made object the farthest away from earth. The space program people operating the mission seem to have great control options, they even “moved software from one chip to another” (link) Apart from the probably gigantic and expensive installation needed to receive and/or send messages from/to that far away from home (23 hours of delay?), are there any safety measures to prevent a potentially malicous actor from sending commands to the probe?
I imagine it’s classified, but NASA being NASA, you know a full risk assessment along these lines exists, probably with dutiful updates as it’s still an active program. It would be fascinating read especially with the updates, with how much the world has changed while the probe remained the same.