I also recommended using an air gap, which physically isolates a computer or local network of computers from the internet. (The name comes from the literal gap of air between the computer and the internet; the word predates wireless networks.)
But this is more complicated than it sounds, and requires explanation.
Since we know that computers connected to the internet are vulnerable to outside hacking, an air gap should protect against those attacks. There are a lot of systems that use — or should use — air gaps: classified military networks, nuclear power plant controls, medical equipment, avionics, and so on.
Osama Bin Laden used one. I hope human rights organizations in repressive countries are doing the same.