JHackguard
The Joomla Extension JHackguard is an old security protection extension which was a simple but effective level of security which prevents access to the Admin Login Page unless you use the secret word.
JHackguard has been removed from the Joomla Extensions Directory and is years out of date so little, if any, support.
There are a selection of tools available now, but one is still free and is a direct replacement AdminExile. (I am not in any way connected with Richey Web)
"AdminExile is a free, battle-tested plugin that once reigned as the #1 security extension in the Joomla Extension Directory. Though eclipsed by tools like AdminTools Pro (which offers similar functionality for a fee), AdminExile remains a robust, no-cost solution to safeguard your backend from drive-by and brute force attacks—keeping honest users honest and everyone else out!"
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.