Add some profile fields that new registrants need to fill in. If your questions are specific, then it will become easier to pick the bots from real people.
Another great hack to add is the 'advanced forum rules' It will stop a lot of bots.
ISbot and vbstopforumspam work nice as well.
EZbounced is a must.
For me the king of spam control is Check4SPAM.

Admin Control Panel (admincp) -> Usergroups -> Usergroup Manager

There should already be a default group named Registered Users. Below it should be an area for Custom Usergroups where you would create a new usergroup such as: Registered Users [Unmoderated].

Then edit the permissions in both the default "Registered Users" (I have renamed that usergroup "Registered Users [Moderated]") and Registered Users [Unmoderated] in the Usergroup Manager so that the first one has its messages moderated and the 2nd one does not. Of course, you can name them whatever you like.

Cheers! -- Rik

I have created those new usergroups, but in 3.6 I don't think there is an option to actually select the usergroup to make it default. So, i installed this: https://vborg.vbsupport.ru/showthread.php?p=1546573 and now all new users are put into moderation.

BUT, now what happens is that vB tells the users that an email has been sent out to be validated, and when they click on that click, it tells them that their account is already validated, so they are already put into that moderation group - but I think this is to do with the actual plugin.

If a user makes 3 posts which are not approved by the admin, does the promotion system still promote them to another usregroup, or do their posts need to be approved first, which are then essentially added to their post count?

An easy way to stop spambots, just 1 file to install and it works:

https://vborg.vbsupport.ru/showthread.php?t=178611

Vb's stock "Registered Users" usersgroup is the default usergroup a new user is automatically (I believe) placed in once their e-mail registration is confirmed. You leave that part alone. You just change the permissions on that usergroup so that its messages are moderated. Then you create a custom usergroup to promote good users to as indicated above.

Hope that helps. -- Rik

Right, it's done.

From what I've discovered there isn't even a need to create a new usergroup. In the vB options there is a setting where you can tell vB to moderate NEW users before they can post, this option also regulates the whole account. So in the meanwhile before they are moved to the main group they are kept to the Awaiting verficaition group.

But I am still discovering how to use the promotion system with this, I just need to know if the promotion system sees UNVERIFIED posts as valid ones.

But the problem with the above method is that it can put users of, becuase once they register and verify their email address, they get Thank you for registering, Test. Your account has been submitted for moderation by an administrator and will be activated shortly. You will be notified by email when this happens. To return to the forums, click here. So it just appears to be an endless set of verification for the user, and it still carries on even after the user has made their first post.