I'm not sure the intention of the code was it for it to be shared on the public internet in plain view without people paying the $20/month subscription. This strategy was an awesome move for Epic Games, please don't make them regret it with stunts like this.

The EULA explicitly says it is forbidden to distribute with non-license holders: https://www.unrealengine.com/eula See 1b.

The cat is out of the bag. Anyway I doubt that this was unforeseen by the Epic team. Somebody was bound to make honest mistake with permissions sooner or later. You just cannot expect a few thousand licensees to not screw up all of the time. And once is all that is needed.

Their are lawyered up enough to prevent anyone from profiting from their IP on the major distribution channels.

Absolutely, but that doesn't make this OK. It looks intentional, the way its been committed under a single commit etc, Epic would have prevented public forking.

It is intentional. The github user has no other activity, and it's an involving conscious process to set the Unreal Engine repository to public.

Shouldn't this be accessible only to those who paid $20[1]?

[1]: https://www.unrealengine.com/ue4-on-github

What prevents someone from creating a game with this and skipping the $20 per month a 5% of gross revenue?

Nothing ... go ahead. If you fail - Epic is not going to miss your token payment. But if you manage to succeed their lawyers will bleed you dry for much more than the 5% of the revenue. Are you going to take your chances?

20 bucks a month over the duration of a development cycle could be pretty significant. This will basically allow people to develop their game to the point where success or failure could be predicted, and Epic will miss out on the development cycle revenues from the failures.

"You can cancel your subscription at any time and keep using the engine, though without monthly updates."

from: https://www.unrealengine.com/register

Even if you cancel your subscription you are obligated by the original agreement to give Epic a royalty that is %5 of gross revenue.

Is it possible to disguise that the game was built with Unreal Engine 4 or is that something that would always be obvious?

Never touched UE, but a few things - engines do have their distinct feel just from gameplay/graphics/shaders etc.

And even if it is possible (which I doubt) any team that is so skilled will just fork the 20 USD

I believe the EULA of the subscription forbids sharing of the source code with non-licensees. So whoever publicly shared the code has violated the EULA, after presumably having given EPic their credit card and personal info. I think this will be taken down shortly. Someone using this code would have to contend with Epic's lawyers. I hope this doesn't ruin the very liberal UE4 licensing for those who abide by the agreement.

The legalities aside, the little bit of code I've browsed through is incredibly well written. And very surprised to see their build system being built in C#. Cool stuff. Almost makes me want to get back into making games.

Don't thank the poster for this, Hacker News is not an illegal software distribution channel.

While the opening of the repo is obviously infringing on Epic copyright, legality of reporting about it and even downloading - their status is very dependent on the country you are in. Also this is not software but a source code.