Joomla Version 1 7 3
From Joomla! Documentation
|Joomla! Version 1.7.3 is NOT the current version. Your website is NOT up-to-date.|
The current short-term support release is 3.5.1. As there have been security updates as well as bug fixes you should upgrade your website as soon as possible. Note that most users should update their sites to version 2.5.0 instead, which is now released.