Writing for The Washington Post's "The Debrief," reporter Barton Gellman looks at last week's NSA story. "The story, based on 160,000 intercepted communications I received from former NSA contractor Edward Snowden, has provoked a lot of questions, objections, and, I think, misunderstandings... NSA surveillance is a complex subject — legally, technically and operationally. We drafted the story carefully and stand by all of it. I want to unpack some of the main points and controversies, sprinkling in new material for context. In this format, I can offer more technical detail about the data set that Snowden provided and the methods we used to analyze it. I will also address some ethical and national security issues we faced. Along the way, I will explain why our story actually understated its findings, clear up speculation about spying on President Obama and fact-check a recent CIA tweet about lost passwords."