/*
MZL Billing Services (c) 2005
Name: Trackback backcheck
Version: 1.0
Description: Trackback Back check for Wordpress 1.5.1.2
More Info: http://www.mein-parteibuch.de/2005/06/16/trackback-spam-filter-eingebaut/
License: Do what you want with it
Installation: Copy/paste in wp-trackback.php before Line beginning with: $commentdata = ...

*/

	$backcheck_enabled=true;
	if(backcheck_enabled){

		$user_agent="trackback link checker";
		$referrer="http://mein-parteibuch.de/";
		
		$ch = curl_init($tb_url);
		
		$curldata="";
		$is_spam=false;
		
		curl_setopt($ch, CURLOPT_HEADER, 0);
		curl_setopt($ch, CURLOPT_TIMEOUT, 3);
		curl_setopt($ch, CURLOPT_NOPROGRESS, 0);
		curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
		
		curl_setopt($ch, CURLOPT_USERAGENT,$user_agent);
		curl_setopt($ch, CURLOPT_REFERER,$referrer);
		
		$curldata.=curl_exec($ch);
		curl_close($ch);
		
		if(stristr($curldata,get_bloginfo('url'))){
		 $is_spam=false;
		} else {
		 $is_spam=true;
		}
		
		if ( $is_spam )
			trackback_response(1, 'Spam protection - we have not found any link pointing to us for this post.');
	
	}