Vladimir Kolesnikov

Like any other software WordPress does have bugs and security vulnerabilities. They get fixed when the developers become aware of them. 
However, sometimes several WordPress releases are vulnerable. The problem is that the developers do not backport security updates to older WordPress releases. 
As a result, those who do not want to upgrade their WordPress installations (for example, because newer WP releases tend to consume more system resources and 
upgrade may result in having to use more expensive hosting) remain vulnerable.
ICS Security Fixes is the plugin for those who do not upgrade their WordPress: the plugin tries to fix known WordPress vulnerabilities 
at that remaining compatible with as many old WordPress releases as possible. 
And though it cannot fix all known vulnerabilities, it makes older WordPress installations more secure.
<h3>Warning</h3>
This plugins requires that PHP 5 be installed. PHP 4 is not supported.

ICS Security Fixes

The plugin tries to fix known WordPress vulnerabilities for older WordPress versions. Warning: For PHP 5 only.

Sean Fisher

This plugin will hide WordPress Admin (/wp-admin/) when a user isn’t logged in. If a user isn’t logged in and they attempt to access WP Admin directly, they will be unable to and it will return a 404. It can also rename the login URL.
Also, you can add HTTP authentication directly from WP Admin and add custom username/password combinations for the HTTP auth or use the WordPress credentials.
This doesn’t touch any .htaccess files or change the WordPress core files. All the CSS/Images under /wp-admin/ are still accessible, just not the .php ones.
If you enable HTTP authentication, it will add HTTP authentication to the PHP files in /wp-admin/.
To contribute to the development, check out <a href="https://github.com/srtfisher/Lockdown-WPAdmin" rel="nofollow ugc">the GitHub Repository</a>.

Lockdown WP Admin

Lockdown WP Admin conceals the administration and login screen from intruders. It can hide WordPress Admin (/wp-admin/) and and login (/wp-login.

ICS Security Fixes vs Lockdown WP Admin