In the original PC and Mac versions of Plants vs. Zombies , the "registration key" or "activation code" was a system used to convert the 60-minute free trial into the full, unrestricted version of the game. Important Note on Modern Versions If you are playing via you do not need a registration key
Websites promising free registration keys often distribute malicious software. Broken Keys: Plants Vs Zombies Registration Key List
There were dozens of them. Strings of letters and numbers like G5RW-8S2K-9L1M B4VZ-7N3Q-1P9X In the original PC and Mac versions of Plants vs