Google is currently sending out a bulk email that looks like this:
Dear webmaster,
You receive this email because you are registered as a website administrator using reCAPTCHA and your site is still using reCAPTCHA v1, which will be disabled on March 31, 2018.
We announced the abandonment of reCAPTCHA v1 in May 2016. Starting in November 2017, a small percentage of reCAPTCHA v1 traffic will begin to display a notification informing users that the old API will be removed soon. Any API v1 calls will not work after March 31, 2018.
To ensure continuous operation, you need to upgrade your site to the current version of reCAPTCHA. You can learn more about reCAPTCHA v2, Invisible reCAPTCHA, and the reCAPTCHA Android API in our Developer Guide. The new APIs are easy to implement and streamline the work of intercepting your users. If you need help, you can participate in the Google RECAPTCHA development team or post to Stack with recaptcha tag.
We hope that your update will be smooth, and we were sure that you will be happy with the results.
Thanks,
ReCAPTCHA support
For those who have built dozens (or hundreds) of sites with ReCAPTCHA over the years, is there an easy way to determine which websites use version 1?
Google Developers ReCAPTCHA (- ), , : https://groups.google.com/forum/#!topic/recaptcha/KRzmHivCtjM