“Some intelligence experts say that the types of files he improperly downloaded at Booz Allen suggest that he had shifted to the offensive side of electronic spying or cyberwarfare, in which the N.S.A. examines other nations’ computer systems to steal information or to prepare attacks. The N.S.A.’s director, Gen. Keith B. Alexander, has encouraged workers to try their skills both defensively and offensively, and moving to offense from defense is a common career pattern, officials say. ”