In 2016, the US was successfully deterred from attacking Russia in cyberspace because of fears of Russian capabilities against the US.
I have two citations for this. The first is from the book Russian Roulette: The Inside Story of Putin’s War on America and the Election of Donald Trump, by Michael Isikoff and David Corn. Here’s the quote:
The principals did discuss cyber responses. The prospect of hitting back with cyber caused trepidation within the deputies and principals meetings. The United States was telling Russia this sort of meddling was unacceptable. If Washington engaged in the same type of covert combat, some of the principals believed, Washington’s demand would mean nothing, and there could be an escalation in cyber warfare. There were concerns that the United States would have more to lose in all-out cyberwar.
“If we got into a tit-for-tat on cyber with the Russians, it would not be to our advantage,” a participant later remarked. “They could do more to damage us in a cyber war or have a greater impact.” In one of the meetings, Clapper said he was worried that Russia might respond with cyberattacks against America’s critical infrastructure — and possibly shut down the electrical grid.
Mr. Rhodes writes he did not learn about the F.B.I. investigation until after leaving office, and then from the news media. Mr. Obama did not impose sanctions on Russia in retaliation for the meddling before the election because he believed it might prompt Moscow into hacking into Election Day vote tabulations. Mr. Obama did impose sanctions after the election but Mr. Rhodes’s suggestion that the targets include President Vladimir V. Putin was rebuffed on the theory that such a move would go too far.
(Via Schneier on Security)
Well said and cited.