As one of the readers requested, I did my best to find ways to stop comment spam on MT powered blogs.

The first thing I did was to go to sixapart/movabletype website and look there. Sure enough, there's a nice selection of anti-comment-spam plugins listed there.

You should definitely get the Captcha plugin, and also Askimet, while HMPassphrase looks good too. You might want to consider getting into the Honeypot project too, if you want to help catch the spammers.

If you run versions of MT older than the current 3.2, you might enjoy getting rid of spam by implementing Jay Allen MT Blacklist tool (just click on MT-Blacklist for 2.5 - 2.661 zip). And if this doesn't cut it, there's always the Avoid Comment Spam 1.01.

Hope any of these helps. If you are not handy with the installation/messing around your MT template structure, I advise you to set up a temporary blog to try things out first. Document your steps to see where you might have went wrong, and read the instructions carefully.