Thread:ConTraZ VII/@comment-25409200-20150707175652/@comment-16087280-20150708004121

I think, this sound is from the files of Valve, but it was cut in HL2. Then the modder reused that sound in that game.

Nexon only can use the sound if it belongs to Valve. If not, it they will face the copyright problem. Also the modder of Afraid of Monsters, as he makes a mod for HL2, not an official game, then he is allowed to use the sound.

So, i think, no need much details.