In the spring of 2016, North Korea's missiles started falling out of the sky, if they even made it that high. In test after test, Kim Jong-un's Musudan missile-the pride of his fleet-was exploding on the launch pad, crashing seconds after launch, or traveling a hundred miles or so before plunging prematurely into the Sea of Japan. After each North Korean test, the Pentagon would announce that it had detected a launch, frequently celebrating the missile's failure. The statements never speculated about what went wrong. But among those inside the Pentagon, the NSA, and the White House who knew about a highly classified US cyber program, each missile that fell into the sea prompted the same urgent question: "Was this because of us?" It was hard to know for any individual launch, but the goal was to delay by several years the day when the North would be able to threaten American cities with nuclear weapons. Cyber was their best hope. The public strategy-which the White House briefly called "strategic patience"-was a failure. No diplomacy was under way. A military strike was far too risky, a nuclear attack too costly. That left only covert action, with the last weapon left in America's arsenal. But the North Koreans had cyber options of their own. Not only did they remake their missile fleet, they seized on tools stolen from deep inside the National Security Agency and turned them on America's allies.... Book jacket.