I've been in a battle with a spammer lately. Got hit one day with 2,000 comments. I've since used a plugin to require commenters to enter a string shown in an image.
Great. Now a spammer (same guy?) is coming at my with trackback-spam.
He pings the correct URL, and voila, his junk messages appear with comments.
I've gotten rid of trackbacks for now, but I do like having them available.
Has anyone else had this problem? What can be done to combat/prevent this?