The team at Joomla has released a new version of their software to address a critical vulnerability in versions 1.5 to 3.4. If you have Joomla installed on your hosting account or server you need to update as quickly as possible to protect your site and the server. You can read more at the following URL's.
https://blog.sucuri.net/2015/12/remote-command-execution-vulnerability-in-joomla.html