For the past few months, an elite hacking group calling itself the Shadow Brokers has sporadically leaked sensitive data from the National Security Agency. On Friday, just when its leaks had appeared to slow, the group released what appears to be its most damaging leak so far: a trove of highly classified hacking tools used to break into various Microsoft systems, along with what it said was evidence that the N.S.A. had infiltrated the backbone of the Middle East’s banking infrastructure.