If you are in the need to deactivate Security Ninja and cannot access the admin side, you can deactivate or remove the plugin via FTP.
Log in to your website and navigate to the folder where the plugins are. This is usually in
You can then rename or delete the plugin folder and this will prevent WordPress from loading the plugin.
Rename or delete either /security-ninja/ or /security-ninja-premium/ depending on which version you have installed.
This will effectively deactivate the plugin.