I got the same WordFence alerts, so at least I don’t think we’ve all been hacked.
Alert generated at Thursday 8th of March 2018 at 07:17:24 PM
Warnings:
* Modified plugin file: wp-content/plugins/wordpress-seo/languages/wordpress-seo-nl_NL.json
* Modified plugin file: wp-content/plugins/wordpress-seo/languages/wordpress-seo-pt_PT.json
* Modified plugin file: wp-content/plugins/wordpress-seo/vendor/autoload_52.php
* Modified plugin file: wp-content/plugins/wordpress-seo/vendor/composer/autoload_real_52.php