I used two different hacks to combat trackback spammers. First, I enabled blacklist checking for moderation. Adding the words sex, rape and incest to the blacklist blocked the majority of trackbacks I was getting. That stopped them going on the site, but I was still getting emails.
I followed anothers advice on these boards to change the default action in /wordpress/wp-admin/moderation.php from "Do nothing" to "Delete" so all I had to do was load the page and hit the submit button at the bottom and they went away.
Later, I noticed all of my spam trackbacks pointed back to the gogof-ck.com domain. This hack to /wordpress/wp-trackback.php made trackbacks that go to that url go away:
Immediately after the
@header('Content-Type: text/xml');
line add:
/* TBK ADD */
$pos = stristr($tb_url, "gogof-ck.com");
if ($pos !== FALSE) {
trackback_response(1, "Damn spammer.");
}
/* TBK ADD end */
Fixed that, at least for that host.