We're reaching out to you today to ensure that you are up to date regarding the latest security issues that may be affecting your website.
The Joomla team released a serious security vulnerability affecting all Joomla versions from 3.4.4 and up. If you’re using one of these versions of Joomla, you’re encouraged to update immediately.
The vulnerability has a high severity as it allows anyone to create a user remotely and specify the desired group permission to it, including administrator.