1) Are you using the vBulletin built-in image verification?
2) Are you doing email verification? I haven't had anything like that amount of spam on the vB forums I work with.
3) Does it appear that the registrations are automated? If so, you may have some options. Unfortunately, most would require some minor coding. Putting in a field hidden with CSS and then processing only forms which have that field blank is one. An even simpler (but easier to defeat) one would be to add a new field in the control panel that says "leave blank" or "what is 4 + 5" and testing for the appropriate value. If a human is setting up the spam, though, these will be too obvious.
Here's the official recommendation set [vbulletin.com] from the authors. You can also check vbulletin.org, the official hack site, for more anti-spam weapons.
1) yeah. it's not done much if anything. 2) I tried. But my users are technically incompetent. Most really shouldn't be allowed around computers. Email verification was causing problems with them as well.
I would suggest... 1. Make sure that the image verification is really working. 2. Go into the admin control panel, and check ALL the checkboxes to vary the image verification font, size, curved letters, etc. 3. If that doesn't work go to vbulletin.org to find an alternative method to image verification.