This update is a security release. Joomla warns us that it is important to upgrade. This release features several improvements to the password storage system designed to help protect the future security of your Joomla! website.  These changes will cause compatibility issues with some 3rd Party Extensions, especially bridges, so proceed with caution if you have lots of applications installed.  The release fixes the following:

Several low-risk security fixes, Improved password storage system, Easier control over Register Globals Emulation, An Itemid backwards compatibility setting, Improved administrative session security, Improved HTTP/HTTPS switchover support.  Download the new Joomla! release