In this context, "prove" means convince a judge of the Cook County court that the NotPetya ransomware was not an ordinary cyber attack, but rather a Russian act

In this context, "prove" means convince a judge of the Cook County court that the NotPetya ransomware was not an ordinary cyber attack, but rather a Russian act of war against the US. I think Zurich's point of view is not untenable. If a Russian military submarine had sunk a Mondelez freighter, would it be an act of war? I think possibly. What if a Russian military cyber hacking squad steals their money with ransomware? Less clear, but still certainly a belligerent act on Russia's part. Of course Zurich will need to present a convincing case that the cyber attack was committed by the Russian government. Will be an interesting case.