From The Daily Beast:

“To take but one extreme example, I have no doubt that if a Russian military unit used a cyber method to destroy the Hoover Dam, we would see that act as no different than had they used a missile,” said Rosenzweig, now a resident senior fellow on cybersecurity and emerging threats at R Street Institute. “The challenge, as it always has been, is in drawing a line where the physical harm becomes so great that America considers itself justified in entering into an armed conflict.”