When downloading a "fixed" executable or a keygen (key generator) for Perfect Uninstaller, you are downloading code that has been modified by an unauthorized third party. You are trusting an anonymous hacker or "cracker" with full administrator access to your computer. Utility software like uninstallers requires deep system permissions to delete files and modify the registry. By installing a cracked version, you are handing the keys to your system's kingdom to an unverified source.