Twice in the past month, National Security Agency cyberweapons stolen from its arsenal have been turned against two very different partners of the United States - Britain and Ukraine. The N.S.A. has [not acknowledged] its role in developing the weapons. White House officials have deflected many questions ... by arguing that the focus should be on the attackers themselves, not the manufacturer of their weapons. The silence is wearing thin for victims of the assaults, as a series of escalating attacks using N.S.A. cyberweapons have hit hospitals, a nuclear site and American businesses. There is growing concern that United States intelligence agencies have rushed to create digital weapons that they cannot keep safe from adversaries or disable once they fall into the wrong hands. On Wednesday, the calls for the agency to address its role in the latest attacks grew louder. Representative Ted Lieu ... who serves on the House Judiciary and Foreign Affairs Committees, urged the N.S.A. to help stop the attacks and to stop hoarding knowledge of the computer vulnerabilities upon which these weapons rely. Brad Smith, the president of Microsoft, said outright that the National Security Agency was the source of the "vulnerabilities" now wreaking havoc. For the American spy agency ... what is unfolding across the world amounts to a digital nightmare. It was as if the Air Force lost some of its most sophisticated missiles and discovered an adversary was launching them against American allies - yet refused to respond, or even to acknowledge that the missiles were built for American use.