Certain things are illegal to do even to the actual soldiers of a country you're at war with. I'd be interested to learn if these rules have been updated since

Certain things are illegal to do even to the actual soldiers of a country you're at war with. I'd be interested to learn if these rules have been updated since the Internet (or ARPANET for that matter) created a whole new realm of possibilities and connections, but I assume not. I think you're right in saying that conventions for this sort of thing are a good idea. The rules will have to be very permissive for aggressors or even friendly nations to actually follow them to some degree, but it could still cover things that directly cost civilian lives like hacking a hospital in a way that risks lives. (Recently someone in Germany died because of malware in a hospital, though the public prosecutor concluded--as expected--there was too little causal evidence to press charges, even if they could find the perpetrator in the first place.)