Google 'CND Response Action' or 'CND-RA'.
'cyber attack' also has a specific meaning, and the Law of War dictates a like for like retaliation.
The Pentagon can't nuke somebody for a cyber attack that causes some emails to be leaked, or some secrets to be stolen.
They can use physical response force in the event that a cyber attack can/will cause actual physical harm, such as disabling a power grid, etc. There is actually a very heated debate about what specifics actions will evoke a physical retaliation to a 'cyber' attack.
If the US or Israel is responsible for Stuxnet, would that be considered an act of war towards Iran? I'm sadly not well-read in either stuxnet or the requirements for it to be considered a cyber-attack.
Not technically - international law today "allows only three situations as legal cause to go to war: out of self-defense, defense of an ally under a mutual defense pact, or sanctioned by the UN" [1].
Iranians may construe stuxnet as an attack that they are hoping to prevent from reoccuring, and thus use the self-defense justification, but 'casus belli' must be the absolute last resort of a nation. Assuming they follow international law that is.
Another important aspect to remember is that retaliation and the use of force does not mean 'war' in and of itself.
The Pentagon can't nuke somebody for a cyber attack that causes some emails to be leaked, or some secrets to be stolen.
They can use physical response force in the event that a cyber attack can/will cause actual physical harm, such as disabling a power grid, etc. There is actually a very heated debate about what specifics actions will evoke a physical retaliation to a 'cyber' attack.