Copy protection is used in King's Quest games I, II, III, IV, V, and VI as a way to prevent theft.
Copy protection in King's Quest I and King's Quest II Edit
In King's Quest I and II, the game has to be loaded from the floppy disk, and the game checks the size of the floppy disk to see if it matches up with what it should be. If the game was copied to another floppy disk or hard drive, the file check fails.
Copy protection in King's Quest III Edit
The page numbers of the spell book which are needed to eventually escape from Manannan are the copy protection.
Copy protection in King's Quest IV Edit
King's Quest IV uses excerpts from a group of paragraphs as copy protection. For example, page 1, 3rd paragraph, 1st word.
Copy protection in King's Quest V Edit
King's Quest V uses special rune spells that had to be answered from the manual after every major section of the game, although the number of times and where it appeared in the game was randomized. This was removed in the CD-ROM version.
Copy protection in King's Quest VI Edit
The Ancient Ones alphabet from the Guidebook to the Land of the Green Isles is used as the copy protection. You must have the alphabet to ascend the Cliffs of Logic successfully. Other puzzles in the game also required clues printed in the guidebook to solve them -- for example, the floor tile trap in the Catacombs. However, many of the solutions are simple enough to be memorized.