Checks for proxies as well as the most common bots for pinterest google and twitter when using the share features.

isBot.php

<?php
function isBot(){
        if(!empty($_SERVER['VIA'])):
            return true;
        endif;
        if(!empty($_SERVER['REMOTE_PORT']) && in_array($_SERVER['REMOTE_PORT'], array(8080,80,6588,8000,3128,553,554))):
            return true;
        endif;
        //if(!empty($_SERVER['REMOTE_ADDR']) && fsockopen($_SERVER['REMOTE_ADDR'], 80, $errno, $errstr, 30)): // this Causes Lag...
           // return false;
        //endif;
        if(empty($_SERVER['HTTP_ACCEPT_ENCODING']) || empty($_SERVER['HTTP_CONNECTION'])):
            return true;
        endif;
        if(!empty($_SERVER['HTTP_VIA'])):
            return true;
        endif;
        if(!empty($_SERVER['FORWARDED'])):
            return true;
        endif;
        if(!empty($_SERVER['USERAGENT_VIA'])):
            return true;
        endif;
        if(!empty($_SERVER['HTTP_X_FORWARDED_FOR'])):
            return true;
        endif;
        if(!empty($_SERVER['HTTP_X_FORWARDED_HOST'])):
            return true;
        endif;
        if(!empty($_SERVER['HTTP_X_FORWARDED_SERVER'])):
            return true;
        endif;
        if(!empty($_SERVER['PROXY_CONNECTION'])):
            return true;
        endif;
        if(!empty($_SERVER['XPROXY_CONNECTION'])):
            return true;
        endif;
        if(!empty($_SERVER['HTTP_PC_REMOTE_ADDR'])):
            return true;
        endif;
        if(!empty($_SERVER['HTTP_CLIENT_IP'])):
            return true;
        endif;
        //Filter Facebook Bot.
        if(strpos($_SERVER['HTTP_USER_AGENT'],'+http://www.facebook.com/externalhit_uatext.php')):
            return true;
        endif;
        //Filter Google+ Snippet.
        if(strpos($_SERVER['HTTP_USER_AGENT'],'+https://developers.google.com/+/web/snippet/')):
            return true;
        endif;
        //Filter Google Bot - Initiates after successful share.
        if(strpos($_SERVER['HTTP_USER_AGENT'],'+http://www.google.com/bot.html')):
            return true;
        endif;
        //Filter Pinterest Bot.
        if(strpos($_SERVER['HTTP_USER_AGENT'],'+http://pinterest.com/')):
            return true;
        endif;
        //Allow only Mozilla and Opera Based Browsers.
        if(!preg_match( '/^(Mozilla|Opera)/', $_SERVER['HTTP_USER_AGENT'])):
            return true;
        endif;
        return false;
}