Note: Everyone who doesn't want to see the things spawned by hackers should have this mod.
Currently this restricts non-master clients from instantiating objects they shouldn't on each client who has this mod installed. This should prevent about 90% of the random lobby hackers you'll experience.
If someone is spawning in things and they are the MasterClient (Spawn in the center of the room before everyone else) then this has to accept those as truth due to the games default behavior of having the host spawn monsters. If you experience someone spawning in anything while using this mod then they are likely the host and you should disconnect from the lobby.
I'm currently working on ways to mitigate people abusing normal remote procedure calls (RPCs) which allows them to do other disruptive things. Keep an eye out for updates.