In the first generation of the online revolution, the question would have seemed absurd. In his new book The Perfect Weapon: War, Sabotage and Fear in the Cyber Age, Belfer Center Senior Fellow David Sanger addresses why that question has become less outlandish.

More than 30 high-tech companies, led by Microsoft and Facebook, announced a set of principles on Tuesday that included a declaration that they would not help any government — including that of the United States — mount cyberattacks against “innocent civilians and enterprises from anywhere,” reflecting Silicon Valley’s effort to separate itself from government cyberwarfare.

Although cyber weapons can usually be employed in a far less lethal manner than guided missiles shot from a drone, they have been deployed less frequently and under rules of engagement that are far less clear, at least to the public.

What started out as a counterintelligence investigation to guard the United States against a hostile foreign power has morphed into a political scandal about what Mr. Trump did, what he said and what he meant by it. 

American officials have long considered Huawei, the Chinese telecommunications giant, a security threat, blocking it from business deals in the United States for fear that the company would create “back doors” in its equipment that could allow the Chinese military or Beijing-backed hackers to steal corporate and government secrets.