reCAPTCHA
Invisible reCAPTCHA

The Invisible reCaptcha extension integrates the new Invisible reCAPTCHA by Google with your WYSIWYG Web Builder site.

Google has recently introduced a new update to their reCAPTCHA service called the Invisible reCAPTCHA. It's based on the same technology as the previous version (the “no captcha reCAPTCHA”), but simplifies the process to remove even the checkbox step. Human users will be let through without seeing the "I'm not a robot" checkbox, while suspicious ones and bots still have to solve the challenges.

More details:
https://www.google.com/recaptcha/intro/invisible.html
Download (Last update: August 18, 2017)
Invisible reCAPTCHA Extension

Requirements:
Works best with WYSIWYG Web Builder 12.1 or higher