Modding is big reason why is Counter-Strike still alive. Modding itself is done by AlliedModders.net where everyone can join (on their Forum). I was playing on GameSites.cz where they have Zombie mode, JailBreak, Trouble in Town, GunGame, Furien, HideNSeek, Capture Flag... Just a lot of different game modes. Why? Because everyone is unique snowflake with unique interests and when you want to get as many of them to play on your servers as possible, you need to modify your servers and not expect them to change. The coding itself is done in language similar to C. There are 2 versions of Counter-Strike 1.6 - Steam and Non-Steam version. The Non-Steam is probably Warez version but it allows everyone to play it (child can get
addictedto it) and you can distinguish Steam and Non-Steam by their unique ID (you can fake Non-Steam ID but Steam ID is based on your Steam Account).