3d_torches can be used, and are being used, to grief protected areas.

[Former user]

In order to make sure that protected areas are safe on my server, i had to add the following code to init.lua, inserted it at line 30

            if minetest.is_protected(p0, placer:get_player_name()) then
                minetest.record_protection_violation(p0, placer:get_player_name())
                return
            end

This effectively prevents 3d_torces from being used for griefing.