If you forgot the secret key, Backdoor can send you an eMail with the correct admin login. The eMail will be sent to the eMail the user is registered at this site.

To request this eMail do the following steps:

• Append "?maillink=<username> to the admin login adress.
  Example: https://www.mydomain.com/administrator?maillink=myusername

If your username is found, AdminExil will send you an eMail to get access to the admin area of the site.

• For whatever reason, it may be the case that you can not access the login page anymore (e.g. lost passphrase).
  Use these steps to disable the plugin from outside:
• Access your server filesystem
  Your access method needs to provide the ability to rename files.
• Navigate to your Joomla website folders, into the plugins/system/backdoor directory.
  Rename backdoor.php - you can rename it to anything, but I like adding an "X" to the filename, like this: Xbackdoor.php.
  I will refer to this filename later, so don't be confused if you renamed it to something else.
• Once renamed, Joomla can't load this file - this means that Backdoor is no longer protecting your site.
• Browse to your /administrator folder, into the Plugin Manager, and disable Backdoor.
• Back in your server filesystem, rename Xbackdoor.php back to backdoor.php.
  By doing this, you can uninstall using the Extension Manager if you so choose, or re-enable the plugin for use once the configuration issues are resolved.