Some of the best hackers in the world work for the NSA. They are the ones who are tasked with hacking into the most—supposedly—impenetrable targets, be it the computers of an Iranian nuclear power facility, or the cellphones of a fugitive terrorist.As far as anyone knows, they don't have a cool sounding name, but they are collectively known as "The Office of Tailored Access Operations," or TAO. They have been called "a squad of plumbers that can be called in when normal access to a target is blocked." And while that name, and that description, might sound underwhelming, they're the NSA's elite-hacking unit, its black bag operations team.Very little is known about TAO, but most of what we know today comes from documents leaked by the former NSA contractor Edward Snowden. To learn more about them, and as part of CYBERWAR, VICELAND's ongoing series on hacking, we travelled to Berlin and London to talk to the journalists who have investigated these sophisticated government hackers in the last few years.