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.

The timing of the leaks coincides with the United States’ recent shift in policy in Syria, which has escalated the conflict with the Syrian government’s main backer, Russia. The Shadow Brokers wrote in broken English in an online post, which cited the American missile attack on a Syrian air base among other reasons for the leak, that after a hiatus, it had returned to leaking because it was upset that President Trump was abandoning “the peoples who getting you elected.”

Among the leaks on Friday was an extensive list of PowerPoint and Excel documents that, if authentic, indicate that the N.S.A. has successfully infiltrated EastNets, a company based in Dubai that helps to manage transactions in the international bank messaging system called Swift.

Swift, short for the Society for Worldwide Interbank Financial Telecommunication, is used by about 11,000 banks to transfer money from one country to another. The vast majority of those banks rely on Swift service bureaus, like EastNets, the largest bureau in the Middle East, to handle their transactions. The latest leaks suggest that, by hacking EastNets, the N.S.A. may have successfully hacked, or at minimum targeted, computers inside some of the biggest banks in the Middle East, including ones in Abu Dhabi and Dubai in the United Arab Emirates; Kuwait; Qatar; Syria; Yemen; and the Palestinian territories. Among the leaked documents was a now-patched N.S.A. road map to hacking Swift’s back-end infrastructure, which could be used by cybercriminals in the future.