JHackguard
I have been using the Joomla Extension Jhackhguard for some years as a simple but effective level of security which prevents access to the Admin Login Page unless you use the secret word.
It has been removed from the Joomla Extensions Directory and as far as I can tell is no longer supported. The latest version is years out of date.
There is a direct replacement called AdminExile which I am now using. (I am not in any way connected with Richey Web)
JHackguard Uninstall Error
There can be an issue with JHackguard when you try to uninstall it.
If you uninstall the PLUGIN first you can then uninstall the Package safely. BUT if you try to uninstall the PACKAGE first it will create an error and lock you out of the Admin area.
How to Fix JHackguard Uninstall Error
If you have uninstalled the package first then it will cause this error and the backend is broken, but there is a way to solve this easily.
You will need to access the Joomla files, which you can do through your usual FTP (Filezilla) or the cPanel File Manager.
Go to the plugins/system folder and delete the folder jhackguard
You will then be able to access the Administrator page and log in as normal.
If you had already set up AdminExile then it will be using the secret word that you set up there, otherwise there will be the standard Administrator access.