I hear they check all your social media these days too.
This is a given. Look at how many of the attacks of late have been preceded by rants on Facebook/Twitter. If you've been a dumbass in public, yep, it counts against you (because this is something that we should need to point out, instead of it being common sense, right?).
And yeah, places like this board count as well, if they can trace you here. If it's out there in the public domain, and you are linked to it, consider it part of your biography (or autobiography, as it were).