User-created modifications

The multi-purpose nature of personal computers often allows users to modify the content of installed games with relative ease. Since console games are generally difficult to modify without a proprietary software development kit, and are often protected by legal and physical barriers against tampering and homebrew software,^[24][25] it is generally easier to modify the personal computer version of games using common, easy-to-obtain software. Users can then distribute their customised version of the game (commonly known as a mod) by any means they choose.
The inclusion of map editors such as UnrealEd with the retail versions of many games, and others that have been made available online such as GtkRadiant, allow users to create modifications for games easily, using tools that are maintained by the games' original developers. In addition, companies such as id Software have released the source code to older game engines, enabling the creation of entirely new games and major changes to existing ones.^[26]
Modding had allowed much of the community to produce game elements that would not normally be provided by the developer of the game, expanding or modifying normal gameplay to varying degrees. Maybe the most notable example is Counter Strike,a mod for Half Life,counter strike turns the initial adventure FPS into a round based,tactical FPS.