cubecolour

WordPress 4.5 added the ability to login using the registered user’s email address in place of the username. When this plugin is active, the ability to login using the email address in place of the username is removed, and the label of the input field is changed to reflect this.

No Login by Email Address

Removes the ability to login using the email address instead of the username.

yoshitech

Change your admin username to whatever you like. Improve your site security and and make life difficult for the hackers. 
Wordpress default administrator username is admin, which makes the job easier for hackers -they only need to find out the password. 
Now, you can change the default admin username to your liking. No one will know it and that improves your site security greatly.
Misc
<ul>
<li><a href="http://www.kupimito.com" rel="nofollow ugc">Plugin website</a></li>
<li><a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=SPY83T4ZJM26Y" rel="nofollow ugc">Donate</a></li>
</ul>

Admin username changer

This plugin does not sufficiently check access permissions, nor does it validate the untrusted user input in any way.
In addition, this plugin can easily cause name conflicts with WordPress core code and other plugins, as it uses too generic names for classes and functions.



Various Security Vulnerabilities

Change your admin username to whatever you like. Improve your site security and make life difficult for the hackers.

No Login by Email Address vs Admin username changer