To the surprise of absolutely nobody.
I have to wonder about the human resources needed to secure a community like this. After a while, it must get just too large, and where an above-ground org can hire from a massive technical labor pool, a community like this would (for obvious reasons) only have access to a much smaller pool of labor. Possibly relying on volunteers or employees that are picked more for their ability to navigate and work securely than for their skillset. The end result could be failures to choose/implement best practices/technologies/solutions/code at any of a million critical points that can give an adversary a way in.
Like, I wonder if it's even theoretically possible to secure a network that illegal and that big in light of what we now about our security organs? I don't see how. I could see individuals staying private maybe, but not entire communities of them. A chain is only as strong as its weakest link.