The defense secretary for a newly elected president is entering his third month in office when a chilling report crosses his desk warning of the catastrophic damage an enemy could visit on the U.S. with a cyberattack. Such an attack, the report warns, could cripple the U.S. economy. It could strike with no warning. It could be launched asymmetrically by an enemy that’s much weaker than the U.S. in traditional military might.