"No open hostilities" is a definition by non-essentials. It's fallacious. As I already said and as you failed to address.
Whether certain people happen to know whether there is an attack or who is behind it does not change anything. A state of knowledge does not change the reality: someone is planning and attacking.
If I had a downvote button, I would exercise it on your steadfast refusal to acknowledge that the Cold War is so-called for the absence of direct military conflict between the armies of the two quarreling states.
Wikipedia does not back your definition, as the Wiki entry leaves room for espionage, sabotage, and other actions that one might consider an "attack" but certainly do not force a declaration of war, mobilization of armies, etc.
Firstly, talking about Wiki definitions is the wrong thing to focus on.
Secondly, the Cold War is a misnomer, the US was very much involved in an open confrontation with the Chinese+Soviets in Korea, and to a lesser extent with their proxies in Vietnam later on.
Yes, the Korean war was fought under the aegis of a resolution issued by the UN security council, but it was a 'hot' war, and part of a broad push against Communist influence.
Surely you don't expect the WP article to list every act that might be compatible with the idea of a "cold war"... I feel you are trolling a bit. Sabotage is still a plausibly deniable act--contrasted with, say, rolling a tank across one's adversary's border.
Stuxnet is a weapon of sabotage, it is fairly direct, and yet it is not the same as an open declaration of war.
"A cold war or cold warfare is a state of conflict between nations that does not involve direct military action but is pursued primarily through economic and political actions, propaganda, acts of espionage or proxy wars waged by surrogates. The surrogates are typically states that are "satellites" of the conflicting nations, i.e., nations allied to them or under their political influence. Opponents in a cold war will often provide economic or military aid, such as weapons, tactical support or military advisors, to lesser nations involved in conflicts with the opposing country."
I.e., this definition does not include direct planned and executed attacks by the nations involved. Continuing:
"The definition which has now become fixed is of a war waged through indirect conflict."
Indirect means indirect, not directly planting viruses that can destroy your factory.
Whether certain people happen to know whether there is an attack or who is behind it does not change anything. A state of knowledge does not change the reality: someone is planning and attacking.