MT-Blacklist
If you have a Movable Type blog, there is a high probability that you have been hit with a recent deluge of comment spam. To keep those spammers out, I highly recommend MT-Blacklist as a simple and effective solution. I understand that spammers are actively avoiding even trying to post to blogs with this plugin in order to avoid being blacklisted (the plugin can share your blacklist with other enabled blogs.)
(If you are hosting a Movable Type blog at one of my domains, and have ever given me your MT password, your blogs have already been immunized and deloused.)
