However this is an active areas of research in both classified and (presumably) non-classified areas. See for example this search: https://scholar.google.com.au/scholar?q=related:KbJLbpaKfCkJ...
My original point was that OPSEC is hard if you're trying to be a topic expert in a short period of time. You don't need NSA tools to attack someone in that situation.
> It seems that it could be made trivial to narrow down lists of suspects by crunching large data sets that contain stuff like SO questions, AC posts on Slashdot, or responses on HN.
Is what XKEYSCORE does (or at least, it's the interface you use to query the above data sets which are collected as part of PRISM and the other programs).
Once again, HN has sent me off into a subject I'd not have found on my own. That's why I like HN as much as I do.