PHP Firewall is a small free PHP script, but secure all websites writen in PHP.

PHP Firewall required PHP 5.
PHP Firewall doesn't use any database, but flatfile system.
It's very small, very simple, really easy to install and fastest.
PHP Firewall have is own logs system and email alert.
No .htaccess file required for betters performances

Security listing
  * XSS protection
  * UNION SQL Injection protection
  * Bads bots protection
  * Bads requests methods protection
  * Small DOS protection
  * Inclusion files protection
  * Santy and others worms protection
  * Server Protection
  * URL Query protection
  * Cookies sanitize
  * Post vars sanitize
  * Get vars sanitize
  * IPs range reserved denied
  * IPs range spam denied

Official website: www.php-firewall.info