I need to choose a license for my project that is an Open Source server emulator for the MMORPG Ragnarök Online, today exists eAthena(with its forks: Cronus and brAthena, for brazilians).
I'm a core developer of Cronus Emulator and we are leaving the eAthena fork to create the emulador using C#, but in Brazil exists a lot of rippers and I need some protection.
Someone can sugest a open-source license that prohibit forks without explicit permission of the author?
Sorry for my bad english(if it was bad).

Because the members need to change the source to create the server the way they want, custom mods, etc. For example the are members that get the RO engine to create a Pokemon game and use Cronus as server base or just to add some improvement ou custom system to the game.

Moving to Business/Law. This is not a software engineering question.