If you are employing someone who is watching porn in an open plan office the problem isn't with your internet filtering system. It is with your employee so just

If you are employing someone who is watching porn in an open plan office the problem isn't with your internet filtering system. It is with your employee so just fire them! If someone is dumb enough to think watching porn in the office is a "good idea" then they are too dumb to be working for you. Just my 2c.