In WordPress 3.7 a new feature was introduced to the core functionality of the application: The automatic updates.
By default, from version 3.7 and above, your WordPress site will update itself when a new minor or security update is released. This means, that if you're on WordPress 3.7.0 and version 3.7.1 is released the application will auto-update itself. On the other hand, if WordPress 3.8 is released (a major version) by default you will have to update it manually.
How to enable major release updates
If you want the WordPress auto-updates to handle major core updates too, you will have to add a single configuration line. To do this, open the wp-config.php file in the root folder of your WordPress installation and add this line to it:
define('WP_AUTO_UPDATE_CORE', true);
How to enable plugins updates
If you want your plugins to be automatically updated by WordPress when a new version is released, you need to add a line to your wp-config.php file, similar to the one above. This time, however, a filter is used for enabling the plugin auto-updates:
add_filter( 'auto_update_plugin', '__return_true' );
How to enable themes updates
If you want WordPress to handle themes updates you need another line added to the wp-config.php file:
add_filter( 'auto_update_theme', '__return_true' );
How to disable core auto-updates but enable plugins and themes auto-updates
If you want to stop the autoupdates of the WordPress core, but to enable them for your Plugins and/or Themes, you can add these lines in the wp-config.php file:
define( 'WP_AUTO_UPDATE_CORE', false );
add_filter( 'auto_update_plugin', '__return_true' );
add_filter( 'auto_update_theme', '__return_true' );
How to completely disable the WordPress auto-updates
If you want to disable the WordPress auto-updates completely, open the wp-config.php file and add this line to it:
define( 'AUTOMATIC_UPDATER_DISABLED', true );