Counter-Strike: Global Offensive (CS:GO) and Team Fortress 2 (Team Fortress 2) source code was leaked to the public on Tuesday. Developer and publisher of the games, Valve, is downplaying the source-code leak, saying it does not see any reason for players to be alarmed or avoid the current builds The code was first posted on the /v/ board on 4Chan, on Tuesday, and led to widespread calls for gamers to not play the games or to uninstall the software from their computers.
Source: https://threatpost.com/valve-confirms-csgo-team-fortress-2-source-code-leak/155092/