function check_referrer() {
    if (!isset($_SERVER['HTTP_REFERER']) || $_SERVER['HTTP_REFERER'] == “”) {
	wp_die( __('Please enable referrers in your browser, or, if you\'re a spammer, bugger off!') );
    }
}
add_action('check_comment_flood', 'check_referrer');
<?xml version="1.0" encoding="UTF-8"?><rss version="2.0"
	xmlns:content="http://purl.org/rss/1.0/modules/content/"
	xmlns:dc="http://purl.org/dc/elements/1.1/"
	xmlns:atom="http://www.w3.org/2005/Atom"
	xmlns:sy="http://purl.org/rss/1.0/modules/syndication/"
	>
<channel>
	<title>Comments on: Let&#8217;s learn a new word</title>
	<atom:link href="http://www.darkhelmetlive.com/blog/2008/08/03/lets-learn-a-new-word/feed" rel="self" type="application/rss+xml" />
	<link>http://www.darkhelmetlive.com/blog/2008/08/03/lets-learn-a-new-word</link>
	<description>programming, video games, love, and in between</description>
	<pubDate>Thu, 08 Jan 2009 23:20:31 +0000</pubDate>
	<generator>http://wordpress.org/?v=2.7</generator>
	<sy:updatePeriod>hourly</sy:updatePeriod>
	<sy:updateFrequency>1</sy:updateFrequency>
		<item>
		<title>By: Wes Cooper</title>
		<link>http://www.darkhelmetlive.com/blog/2008/08/03/lets-learn-a-new-word/comment-page-1#comment-496</link>
		<dc:creator>Wes Cooper</dc:creator>
		<pubDate>Mon, 04 Aug 2008 14:05:21 +0000</pubDate>
		<guid isPermaLink="false">http://www.darkhelmetlive.com/blog/?p=297#comment-496</guid>
		<description>What's happening to Internet radio does seem unfair.</description>
		<content:encoded><![CDATA[<p>What&#8217;s happening to Internet radio does seem unfair.</p>
]]></content:encoded>
	</item>
</channel>
</rss>