How can I prevent "spam" user registrations?
Plugins:


Snaptcha (private beta)
Works with the User Registration Form, Contact Form Plugin and Sprout Forms Plugin
Invisible Captcha (private beta)  


.

Config:

If you don't mind having a few spam-users in your list. Just add purgePendingUsersDuration to your config.

This will purge all users which haven't been activated for x time.