When armed Libyan citizens attacked the Benghazi compound, which was American soil, and murdered the ambassador, that was an overt act of war. The President did nothing.The Czar is precisely correct that nothing will happen. I will go further and say that a US company getting hacked by someone overseas is a really really really bad reason to go to war. It's far too easy for a clever attacker to implicate a third party, pulling us into regional conflicts that we have no business in.
Given the Sony hack was much less catastrophic in terms of lives lost, the President will again do nothing. Since he blamed the compound attack on a YouTube video, perhaps he will blame the Sony hack on the popularity of Korean barbecue places.
And quite frankly, there's quite a moral hazard here: many people think that Sony had a terrible information security program, because they didn't want to spend the money. Fine, that's their business decision. However, the US Marines shouldn't be a backstop for them trimming IT costs.
Are there cyber attacks that could cross this boundary? Sure - shutting down a major part of the power grid would qualify in my book. But not Sony.