One slide from a May 2010 NSA presentation on getting data from smartphones – breathlessly titled "Golden Nugget!" – sets out the agency's "perfect scenario": "Target uploading photo to a social media site taken with a mobile device. What can we get?" To me, this is quite telling. The NSA is not considering what data they need to achieve their mission, and then trying to find that data. Instead, they're just looking…
Once someone is a target, investigating them in general is legitimate, assuming that there is justification for regarding them as such.