This is the undisputed domain of General Keith Alexander, a man few even in Washington would likely recognize. Never before has anyone in America’s intelligence sphere come close to his degree of power, the number of people under his command, the expanse of his rule, the length of his reign, or the depth of his secrecy. A four-star Army general, his authority extends across three domains: He is director of the world’s largest intelligence service, the National Security Agency; chief of the Central Security Service; and commander of the US Cyber Command. As such, he has his own secret military, presiding over the Navy’s 10th Fleet, the 24th Air Force, and the Second Army.
     Alexander runs the nation’s cyberwar efforts, an empire he      has built over the past eight years by insisting that the      US’s inherent vulnerability to digital attacks requires him      to amass more and more authority over the data zipping      around the globe. In his telling, the threat is so      mind-bogglingly huge that the nation has little option but      to eventually put the entire civilian Internet under his      protection, requiring tweets and emails to pass through his      filters, and putting the kill switch under the government’s      forefinger. “What we see is an increasing level of activity      on the networks,” he said at a recent security conference in      Canada. “I am concerned that this is going to break a      threshold where the private sector can no longer handle it      and the government is going to have to step in.”
In its      tightly controlled public relations, the NSA has focused      attention on the threat of cyberattack against the US—the      vulnerability of critical infrastructure like power plants      and water systems, the susceptibility of the military’s      command and control structure, the dependence of the economy      on the Internet’s smooth functioning. Defense against these      threats was the paramount mission trumpeted by NSA brass at      congressional hearings and hashed over at security      conferences.
But      there is a flip side to this equation that is rarely      mentioned: The military has for years been developing      offensive capabilities, giving it the power not just to      defend the US but to assail its foes. Using so-called      cyber-kinetic attacks, Alexander and his forces now have the      capability to physically destroy an adversary’s equipment      and infrastructure, and potentially even to kill.      Alexander—who declined to be interviewed for this      article—has concluded that such cyberweapons are as crucial      to 21st-century warfare as nuclear arms were in the 20th.
 
