Late last night/early this morning an update to Joomla! was released–bringing the current version to 1.5.16. The update fixes several low to moderate security vulnerabilities, so it's advisable that you upgrade as soon as possible. You can read more about these vulnerabilities here.

Make sure you download Joomla! 1.5.16 and update soon.

If the idea of uploading the update and overwriting files makes you a bit squeamish, you should check out Update Manager for Joomla! It's a simple and easy to use tool that makes the process so incredibly easy.

*Important* - When updating there is the potential for you to lock yourself out of your Joomla! Administrator area if you're not careful. Before updating, simply make sure you

1. login, go to your "Global Configuration".
2. click on the "System" tab, and then select "Database" from the drop-down under "Sessions".
3. Then click save.

You should be safe from getting locked out now.

If you're reading this after having been locked out of your administrator area, don't worry, there's an easy fix.

1. Find and open the /libraries/joomla/applications/application.php. Open it up and on line 533 comment out the code you find there. So change: 
 $session->fork(); 
to
/* $session->fork(); */
2. Then login to your Administrator Area, go to "Global Configuration", click on the "System" tab, and select "Database" from the drop-down under "Sessions" and click save.
3. Then don't forget to go back to your application.php file and undo the what you did in step 1, changing line 533 back to look like: $session->fork();