Xash is uncommercial educational open source project, which is 8 years old. Most of its' parts were redesigned from scratch. Some coding parts are borrowed from Valve to make new engine compatible with GoldSource maps and mods, but the author of Xash3D did no any cracking actions for this. And he have fixed a lot of promblems of old GoldSource engine in Xash3D by everyday working on a code's improving. But someone still prefers to think, that all he is doing those 8 years it's cracking and stealing. But stable 3D engine with many changes and specific features can not be created by copy/paste. Every good programmer knows it. Even if Xash have some doubts about it's legality, it still have no claims about this from Valve. Because it don't interfere any commercial interests of Valve. This is project for fans and oldphages. But if you still have any doubts, OK, do NOT use it.