Spam registrations unstoppable
 

Hi,

In the last two days I've had hundreds of new user registrations. They all look valid, but since none of them has actually posted anything and this level of registration is unusual, I'm sure they are some sort of spam.

These users can't do anything much other than post on the forums (email and PM is disabled initially).

I was using 3.6.8, I've now upgrade to 3.8.6 PL 1.

I've switched to reCaptcha, and added an extra field.

reCaptcha made no difference to the rate, and I had 6 registrations within 10 minutes of adding the extra field!

Questions:

1. What is the purpose of these bogus registrations?
2. Is there nothing I can do to stop this? Are they using humans to solve the reCaptcha and enter the extra field?

Moderating new users is not appropriate for my forum.

Please HELP!

regards,
RR