Short of a direct military threat on the US, I think that the military would disobey such an order up and down the line. Yeah, a few rogue generals would try to carry it out, but the core leadership and enlisted personnel, I think, would outright refuse. It would be a risk, but I don't think that false allegations of "hacking" are grounds for ANY military action.
The problem here is that Obama prefers to use our Spec Ops. Those guys usually have no idea what or who they are attacking. They just get coordinates and are told what to destroy. A couple have told me they had no idea what they were actually attacking until they read about it later.