Here is tutorial on how to disable WordPress automatic updates. Since WordPress 3.7 there is a feature called Background Updates that will update your WordPress automatically.
This updates by default are applied in minor updated, if turned on it will upgrade from 3.7 to 3.7.1, 3.7.2 etc. but will not upgrade on major releases like from 3.7.x to 3.8
This settings are defined with the WP_AUTO_UPDATE_CORE option in your wp-config.php file. The default settings are to update minor updates as explained above.
Disable WordPress Automatic Updates
You can Disable WordPress Automatic Updates by adding this line in your wp-c0nfig.php. This
/* Automatic updates */ define( 'WP_AUTO_UPDATE_CORE', false );
Enable Minor WordPress Automatic Updates
If you want to apply minor automatic updates you don’t have to change anything or you can add this line in your wp-config.php file. This will update minor releases as explained above.
/* Automatic updates */ define( 'WP_AUTO_UPDATE_CORE', minor );
Enable WordPress Automatic Updates
You can Enable WordPress Automatic Updates by adding this line in your wp-c0nfig.php. This will turn on ALL updates, i really don’t recommend this but if you are filling lucky you can do this and leave everything updates itself.
/* Automatic updates */ define( 'WP_AUTO_UPDATE_CORE', true );
For most of the sites minor updates are OK.
You can disable WordPress automatic updates on websites with a lot of custom code where you need full control on your updates when you need to do a test run on a new release and then update.
And if you enable ALL WordPress automatic updates your WordPress will update itself automatically on every release. I really don’t recommend this because you can run into problems with your plugins, themes and custom code, and your site can go offline without you knowing.
More technical post aimed for developers: The definitive guide to disabling auto updates in WordPress 3.7