Add/Change SECRET_KEY in wp-config.php for WP 2.5.x installs
The SECRET_KEY value in the wp-config.php file is a new addition since WordPress 2.5, and adds extra security to your blog. On older installs, upgrading does not add the key, so this plugin was written to add the key transparently, or change the key.
It is not needed on older blogs (before 2.5). Also, brand new installs will add the key automatically, so it's only needed then if you wish to change the key periodically.