As a programmer I would suggest the problem is the "Math Question" field is far too easy to defeat as a tool for separating humans from spambots.

As a professional programmer, I can write a simple Visual Basic Program that can read the raw HTML text from your website, parse out the question, and formulate an automated reply to defeat your human tester.

I suspect this is exactly how you are being overwhelmed by apparently "gay" and supremely irritating spambots - although not by me.

A far stronger technique would be the "distorted bitmap" text that OCR based software cannot effectively read but humans can. Many websites use this technique these days (such as the Orlando Sentinel) to separate the beings from the bots.

I would believe that such modules are available both for Drupal and Joomla.

I am working on setting up a Joomla based site myself and find it a lot easier to understand than the Drupal CMS.

I hope things start improving soon and I sent you a piece this morning (although it is likely too long) that I hope you can use in some fashion.