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Well, yesterday's foolproof method of defeating trackback spam is today's old news. Seriously no less than 24 hours after I proclaimed victory, I have started getting trackback spam that defeats the validation method by maintaining a list of the links, rotating out the URLs as it spams them -- on the same page as their ads, or whatever content they are pimping in their spam.

For now I can just blacklist this IP, but a botnet will soon be employed to do its dirtywork. Because trackbacks are a process that by definition is automated, it's particularly difficult to stop, since any turing-test type validation is out of the question.

And so the battle rages on.