By basing professional hiring decisions on candidates
While I am a senior linux engineer, I also contribute to the technical hiring of candidates. "professional hiring decisions on candidates" do not involve how technical someone is but how they fit into the team and organisation. There is no room for a double agent in a work place and those double agents are highly likely to be those who are antagonistic in their forum posts.
Ocean: A body of water occupying about two-thirds of a world made for man -- who has no gills. -- Ambrose Bierce