If you use the Jetpack plugin on your site, please update today.
We've just released new versions of the plugin to address a security vulnerability. Your site will be automatically updated to a safe version in the next few hours, but you can of course update manually.
Read more about this here: https://jetpack.com/blog/jetpack-13-9-1-critical-security-update/
Or reply to this post if you have any questions!