I, too, need the “five year old” explanation. I just got hit with trackback spam. (WP 1.2 installation). I’ve deleted wp-trackback.php to prevent future problems.
Here’s where I’m the confused 5-year old. Unlike comment spam (sent to moderation in my installation) there appears to be nothing to delete on my WP website for trackback spam. Is that right? I want to be sure that I am not advertising online poker.