I have a site that uses an old custom comments script, and recently I began getting tons of spam comments there as well. I tried blocking IP addresses and bad words, but that didn’t work for very long. So I ended up changing the system so that it’s moderated (doesn’t post the comment unless I approve them, and sends an email with a link to do so).
It’s a drag that we have to put up with such pathetic and anti-social behavior, but this did solve the problem.
