wordpress security: avoid requests from malicious urls

gistfile1.php

global $user_ID;
if($user_ID) {
    if(!current_user_can('administrator')) {
        if (strlen($_SERVER['REQUEST_URI']) > 255 ||
            stripos($_SERVER['REQUEST_URI'], "eval(") ||
            stripos($_SERVER['REQUEST_URI'], "CONCAT") ||
            stripos($_SERVER['REQUEST_URI'], "UNION+SELECT") ||
            stripos($_SERVER['REQUEST_URI'], "base64")) {
                @header("HTTP/1.1 414 Request-URI Too Long");
                @header("Status: 414 Request-URI Too Long");
                @header("Connection: Close");
                @exit;
        }
    }
}