[alpine spirit]

Here is what I did on my board... from Vb.org I think it was

How to add an extra registration question to frustrate human-assisted bot registration?

AdminCP -> User Profile Fields -> Add New User Profile Field

Profile Field Type: Single-Line Text Field

Use the following information when creating the Profile Field:
Title: Can you spell?
(Note: Adjust the title to the question you want to ask)
Description: Enter the first character of the word "Monkey"
(Note: Adjust the question. Don't use this example as it would be quickly picked up by bot registrations)
Default Value: B
(Note: anything but a valid answer)
Field Required: Yes at registration
Field Editable by User: Only at registration
Private Field: Yes
Field Searchable on Members List: No
Show on Members List: No
Regular Expression: ^[mM]$
(Note: this expression would only allow a 'm' or 'M' as valid answers, adjust to your needs)

This is not a fool proof solution, but will probably limit the number of semi-automated registrations.

FYI.. It killed the bots (50 a day), its been almost 36 hours and no spammer registrations, 3 legit registrations.