I've been seeing huge amounts of spam trackbacks on my site. I don't see any comment spam, because I require registration before comments can be posted. But when I have thousands of spam trackbacks at a time, the current facilities aren't sufficient. What I instead do is::
DELETE FROM trackback_received WHERE status = 0;
Which deletes any unapproved trackbacks. If there are any legitimate ones in there, but there's too many spamm'd ones, then I don't have time to delete the spamm'd ones individually. So away they all go, whether or not they're legit.
I tried searching here and didn't come up with much in the way of discussion.
I did install the spam.module and it ties with the trackback.module so that there is bayesian filtering. Hence, the majority of the trackbacks I'm receiving are marked as spam alright.
HOWEVER ... with the current user interface, I still have to individually delete them. There's no effective batch mode delete in trackback.module. It would be great if there were a "delete all" button or "select all" which could let one select all the trackbacks shown on the page letting you easily remove them in large chunks. Right now the UI is clumsy in that it requires to you click on 40 checkboxes per page, then scroll back to the top and select "delete selected trackbacks" and click the submit button.
In any case, I did a bit of research about spam trackback fighting methods. The results are here: