Reverse engineering is not illegal nor is emulating a reverse engineered protocol. If you're just doing some freelance server work, you're generally not doing anything illegal; you can totally throw a fit about not being paid. But, most people simply won't. Distribution of game assets and the game client are another story. But, regardless, if they were being paid for this, their rights both morally and legally go out the window.
If they were getting paid, it doesn't really matter how the server was being managed. It's still really not cool to post work that doesn't belong to them. Once you start taking cash for code, all your rights to it go out the window unless explicitly stated otherwise.
Moscow, Russian Federation
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