Cyberattacks are different then sending a warship or dropping a bomb though. They are harder to attribute and anyone knowledgeable and willing to the spend the time can carry them out. There have long been cyberattacks by criminals on companies in other countries, but attacks by individuals on governments are also possible as we now see. It seems likely others will emulate this and there is no obvious way to stop it from happening. It may be illegal but you have to find the person responsible first. Current cyberdefenses obviously are porous. Warfare used to be the domain of the state mainly because only the state had the capabilities (and some corporations have had and used similar capabilites, like oil companies with their own private armies). An individual could travel somewhere and start throwing bombs but the amount of damage they could do was small. Instead of a DDoS attack this guy could have decided to brick all computers in North Korea. I don't see a way these kinds of attacks can be stopped and they seem likely to cause a lot of havoc in the world. Basically, imagine ransomware with a political motive behind it launched by individuals with a goal of destruction rather than Bitcoin. It's actually kind of surprising there haven't already been many instances of it, or maybe there have.