I want to prevent people from ripping off my maps.
I know you don't add plugins that often, but please add it!
I'll vouch for this. I agree that people would do anything to rip people off for the benefit of their own.
You can't prevent worlds getting downloaded, people already download your worlds by walking around in them.
Really, the only way to stop people from downloading your worlds is to prevent chunk packets to be send to the player, but this will leave them in a voidworld.