Disable update checking of WordPress
When you designing a website for client with WordPress, you may not want your client click the “Upgrade” button for any reasons (mostly, by curiosity). We all know that it may cause unusable of customized theme. Here’s how to disable it. Open functions.php of your theme and add following lines.
add_filter('pre_site_transient_update_core', create_function('$a', "return null;"));