ylsine

Do you have a blog that really only want ready by humans? Do think that 
<a href="http://google.com/" rel="nofollow ugc">robots</a> should never be able to read your blog, even if they ignore your robots.txt? Is privacy your number one concern? Do your friends think of you as “that total privacy nut…you know too much so.”? Then this plugin is for you. The 404er will make every public page of your blog return a <a href="http://en.wikipedia.org/wiki/HTTP_404" rel="nofollow ugc">404</a> instead of the normal <a href="http://en.wikipedia.org/wiki/List_of_HTTP_status_codes#2xx_Success" rel="nofollow ugc">200</a>. Yes, you could use the normal <a href="https://codex.wordpress.org/Settings_Privacy_SubPanel" rel="nofollow ugc">privacy subpanel</a>, but that would be sooo pedestrian. Step up to the real (excessive, <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.5" rel="nofollow ugc">RFC abbusing</a>) 404!
Note: If you did not detect any humor in the above text or you do not know what a 404 is, then, in all caps, DO NOT INSTALL THIS PLUGIN!

The 404er

This plugin will send a 404 header for every public page on your blog.

atmosphear

Send an “HTTP/1.1 403 Forbidden” header on a failed login instead of “HTTP/1.1 200 OK”, which is the WordPress default header on failed login. This is a tremendously simple plugin that does only that and absolutely nothing else.
The purpose of this plugin is to provide a way to allow external tools like fail2ban to get a message of a failed login e.g. to prevent a brute-force attack on a firewall level.
For the public domain.
Uses PHP5.3 anonymous functions and will not work on earlier versions of PHP

HTTP/1.1 403 Forbidden header on a failed login

Send an "HTTP/1.1 403 Forbidden" header on a failed login instead of the default "HTTP/1.1 200 OK"

The 404er vs HTTP/1.1 403 Forbidden header on a failed login