Terrorism is generally the use of tactics that inflict terror on a civilian population to get a desired effect. The specific exclusion of official government and military actions is motivated reasoning on the part of government officials, who prefer to use nicer euphemisms to describe their own actions.
> on 28 March 1945 the Prime Minister, Winston Churchill, sent a memo by telegram to General Ismay for the British Chiefs of Staff and the Chief of the Air Staff in which he started with the sentence "It seems to me that the moment has come when the question of bombing of German cities simply for the sake of increasing the terror, though under other pretexts, should be reviewed...."[13][14] Under pressure from the Chiefs of Staff and in response to the views expressed by Chief of the Air Staff Sir Charles Portal, and the head of Bomber Command, Arthur "Bomber" Harris, among others, Churchill withdrew his memo and issued a new one.[14] This was completed on 1 April 1945 and started instead with the usual euphemism used when referring to strategic bombing: "It seems to me that the moment has come when the question of the so called 'area-bombing' of German cities should be reviewed from the point of view of our own interests....".[15]
(Incidentally, I think you have to stretch even my definition of terrorism to include hacking.. having your power turn off or your bank shut down by hackers is certainly destructive and disruptive, but terror inducing? That's a stretch. It's not like you're trembling in fear wondering if a bomb is going to crash through your roof tonight.)