Setting up the reCAPTCHA function is a great way to reduce spam accounts being created automatically
Step 1. Login as an Administrator and click Site Administration.
Step 2. Click Plugins.
Step 3. Click Email-based self-registration settings.
Step 4. Make sure that Enable reCAPTCHA element is set to “Yes”.
Step 5. Click Save changes.
Step 6. Sign up to google reCAPTCHA and get the public/private keys.
Step 7. Click Site Administration
Step 8. Click Plugins
Step 9. Click Manage authentication
Step 10. Scroll down to enter the ReCAPTCHA site key.
Step 11. Enter the ReCAPTCHA secret key.
Step 12. Click Save changes.