Minecraft's private server owners have always been free to modify and/or monetize the game as they see fit, but it seems that this bit the game's creator Markus "Notch" Persson in the behind in more than one occasion, forcing him to enact new rules regarding server monetization.
"Some privately run Minecraft servers do charge for in-game items, for xp boosts, for access to certain game modes. Some of them even charge quite a lot," he explained on his blog. "I don't even know how many emails we've gotten from parents, asking for their hundred dollars back their kid spent on an item pack on a server we have no control over."
The new monetization rules are meant to thwart such accusations in the future. In a nutshell, Notch is asking private server owners to make it clear to their customers that the server isn't controlled by Mojang, not to sell items that impact gameplay, and not to charge real-world money for in-game money.
