[eco]

That's not actually true. Carmack uploaded the source for the level editor and utilities for modders to use. The modding community just made much better and easier to use tools. .wad files were also created specifically to encourage modding and make it non-destructive.

Excerpt from Masters of Doom:

> Though Carmack and Romero were intrigued and inspired by these actions, they were concerned over the destructive quality of the mods. Players had to erase the original Wolfenstein code and replace it with their own images; once a Nazi was changed into Barney, there was no way to bring the Nazi back quickly. For Doom, Carmack organized the data so players could replace sound and graphics in a nondestructive manner. He created a subsystem that separated the media data, called WADs (an acronym suggested by Tom Hall, it stood for Where’s All the Data?), from the main program. Every time someone booted up the game, the program would look for the WAD file of sounds and images to load in. This way, someone could simply point the main program to a different WAD without damaging the original contents. Carmack would also upload the source code for the Doom level-editing and utilities program so that the hackers could have the proper tools with which to create new stuff for the game.