Mutually assured destruction is a hell of a deterrent.
Full on cyber war to me looks like a erased economy by zeroing every asset and liability in the banks and funds, with pre-corrupted backups. It looks like bricked firmware on every router, industrial process controller, police/fire radio system, public utilities, even vehicles. It would be like an EMP hit. With nobody getting paid, no emergency services or utilities, public unrest would do all the work.
If they do it right, it's like Einstein's quote about world war IV will be fought with sticks and stones.
Why brick routers and SCADA systems, and not spread malware or cause damage?
Why shut down the police/fire radio system, and not air false calls?
Chaos and misinformation is more useful than simply shutting it all down.
Further: US oligarchy[1][2]/establishment/(self proclaimed) elite blames Russia for every leak where they look bad. As if there are no real US American patriots who, unsatisfied with the course that same oligarchy has taken in the last 25 years, want to expose it and try to change it.
[1] http://www.rollingstone.com/politics/videos/jimmy-carter-u-s...