OK - have DL'd and installed the module for SMF 1.1.16. It "seems" to be working as my forum registration notifications from bots have dropped dramatically - THANK YOU.
Glad it seems to be working for you.

Just one question - because of the sheer volume that had been registering (25+ every hour) how do I know the daily count of attempted registrations? Can't see any chamges or notification indicators on the Admin side of SMF.
This truly seems to have stopped the bots and I would not mind getting an API Key but am uncomfortable not having a "gauge" to determine what the daily attempts / lookups are so I acquire the correct size of key.
DW
1) You could install some simple code to log attempts or send an email for each failed attempt.
2) API keys are free.
3) There's only one "size" of key, apart from corporate or "sponsor" users.