So, you just updated your site with WordPress 3.7 (or newer), and you noticed that one of the new features is automatic background updates. The feature will updated WordPress core and translations files, but it will also allow you to automatic update themes and plugins.
There are also reasons why WordPress auto updates will not work, If you want to find out why, you can use the Background Update Tester plugin.
But you are here to learn how to prevent the updates. There are a couple of options that you can add to the wp-config.php file, depending on what updates you want to allow or prevent.
Core updates for minor releases (default):
define( 'WP_AUTO_UPDATE_CORE', 'minor' );
Core updates, including minor and major:
define( 'WP_AUTO_UPDATE_CORE', true );
Disables all core updates:
define( 'WP_AUTO_UPDATE_CORE', false );
Completely disable all updates
define( 'AUTOMATIC_UPDATER_DISABLED', true );
Disable all update and file modifications (Our Favorite)
define( 'DISALLOW_FILE_MODS', true );
The setting above will completely disable updates and even prevent file modifications by any user including administrator until the option is removed or disabled.