Getting too many human spammers - how do I stop them?

[MSUKForum]

My forum is starting to get over run by spammers who are real people registering, they bypass the recaptcha and a knowledge required security question, then post a few vague things to topics, like "that's cool" etc before eventually posting an advert with a link in.

They seem like real people doing this and I don't know how to counter it, any suggestions?

[opentype]

Moderating the first two posts of every new member and blocking the IP once they posted spam. They will eventually give up. 

[Miss_B]

You can use Automatic Content Moderation option in your Admin Panel for that. It will help a lot.