reCAPTCHA v1 will not work after March 31, 2018

What is reCaptcha?

reCAPTCHA is a free service offered by Google that protects your website from spam and abuse. reCAPTCHA uses an advanced risk analysis engine and adaptive CAPTCHAs to keep automated software from engaging in abusive activities on your site. It does this while letting your valid users create accounts and pass through with ease. 

What does "reCAPTCHA v1 will not work " mean?

If your site has reCaptcha saved in your admin settings then after March 31, 2018 new users will not be able to create accounts on your site. This applies to all license holders.

What should I do?

You should upgrade to reCAPTCHA v2 immediately. It's very easy to upgrade, just follow the steps listed here