Having a reCAPTCHA powered registration on your website can help you dramatically reduce user registration spam.
Once you add the reCAPTCHA field to the Manage Fields list in Profile Builder, under the field options, you will be able to select the forms which will have reCAPTCHA verification enabled.
Adding reCAPTCHA to Profile Builder front-end forms
The first set of options allows you to choose which Profile Builder forms should display the reCAPTCHA verification.
By default, only the Register form has reCAPTCHA verification enabled, but you can also add reCAPTCHA to Login and Lost Password front-end forms by checking the corresponding options.
Having a reCAPTCHA verification in place on the Login and Lost Password forms is a good way to improve your website security and protect yourself against brute force attacks.
Adding reCAPTCHA to WordPress Register, Login and Lost Password forms
Profile Builder allows you to also add reCAPTCHA to the default WordPress Register, Login and Lost Password forms as well.
By default, the WordPress Register form will have reCAPTCHA enabled, but you can choose to also add it to the (back-end) WP Login and Recover Password forms.
With the improved reCAPTCHA field from Profile Builder, you now have full control over which forms (both back-end WP default forms as well as front-end Profile Builder forms) should display the No CAPTCHA reCAPTCHA verification.
Note: The improved reCAPTCHA field is available in Profile Builder premium versions (both Hobbyist and PRO), starting with version 2.1.6.