Telling the world about your Joomla version in your HTML code is like inviting malicious attacks to your own doorstep. It’s like saying, “Hey, I have Joomla version 1.5 – that is known for the following vulnerabilities (add list of vulnerabilities here) – would you like to attack me?” If you want to check that you are exposing your Joomla version to the world, then just go to your website using Firefox, right click on the page, and then click on “View Page Source”. If you see something like the following line:
then you are exposing your Joomla version. Check this post on how to hide your Joomla version.