Fifteen months into a wide-ranging investigation by the agency's counterintelligence arm and the F.B.I., officials still do not know whether the N.S.A. is the victim of a brilliantly executed hack, with Russia as the most likely perpetrator, an insider's leak, or both. Three employees have been arrested since 2015 for taking classified files, but there is fear that one or more leakers may still be in place. And there is broad agreement that the damage from the Shadow Brokers already far exceeds the harm to American intelligence done by Edward J. Snowden, the former N.S.A. contractor who fled with four laptops of classified material in 2013.
Mr. Snowden's cascade of disclosures to journalists and his defiant public stance drew far more media coverage than this new breach. But Mr. Snowden released code words, while the Shadow Brokers have released the actual code.