It is not illegal to download the Game Killer app for Android software. However, the hacking of applications, its main function, is frowned upon by many.
The Game Killer app is available for download free of charge and is not illegal in any way, as of 2015. The app is designed to help users hack into Android software and applications, allowing for the changing, tweaking and editing of the application software. However, the practice of hacking is not allowed as it is an infringement upon the rights and protection of both the affected apps and their creators. Users are not allowed to misuse the app.