A code wheel is a type of copy protection used on older computer games, often those published in the late 1980s and early 1990s. It evolved from the original "manual protection" system in which the program would require the user to enter a specific word from the manual before the game would start up or continue beyond a certain point. This system was popular because it allowed the actual media to be backed up and replaced freely while retaining security, but with the increased availability of photocopiers, those wishing to distribute the games simply started copying their manuals as well to defeat the measure.