The following is a trick to prevent spamming by bots in Movable Type 2.x. While this blog doesn’t run MT, several other blogs I manage still do, and I have found this to be a surprisingly effective method to disable automated spam bots.
Rename the post field in your MT templates from “post” to something else. You will have to do this in all of your templates that have a comment form. Then go to MT\App\Comments and on line 29 modify the “post” value to your new field name. Whatever you do, if you use MT, be sure to get the latest version of MT-Blacklist. (This tactic can be used with almost any scripted comment system, if you aren’t afraid to get into its guts and redo changes after updating.)

Now a tip for WordPress users: unless you get frequent legitimate comments with many links, lower the default value of links allowed without moderation at Options ->Discussion->Comment Moderation. You can then use the “Mass Edit Mode” to delete spam posts. Also be sure to update your default spam word lists from the WP-Wiki.