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Everybody does it. When faced with a challenge, it's perfectly natural to look for an example that someone created earlier, and then borrow, adapt and change it to suit your needs. It looks like the team behind The War Z forgot that the most important thing to do in this situation is to modify all of the appropriate bits, and cover your tracks.
It seems that the License Agreement for The War Z contains snippets of the Terms of Service for League of Legends. This little slip up would be embarrassing enough, but it gets worse: Sergey Titov, the founder of The War Z developer Arktos Entertainment Group previously worked for Riot Games, the company that owns League of Legends. Oops.
According to a Redditor who actually read both documents, the similarities were striking. Other than the two files being fundamentally the same (with the title changed), there were a couple of obvious, undeniable issues, like this one included in the installer for The War Z:
Now, when we say that "everybody does it" in terms of copy/pasting form documents and other bits and pieces, we don't just mean college students who left that essay a bit late. We mean just about everyone - including top lawyers. Once you have a legal document that works for you, it's in your best interests to avoid changes, even when that means using the same template for multiple clients.
So - even though technically Arktos could maybe get in trouble for copyright infringement, it seems unlikely. Legally speaking, it's somewhat accepted, although generally a good idea to tidy up all traces of the original document.
This means that while The War Z has egg on its face, and the developers are being painted as particularly lazy people, it might not be all bad for Arktos and the game. That said, it's probably not going to be much fun for the person who wrote up the License Agreement for The War Z, who might have just found themselves in quite the spot of bother.