Index: wp-includes/update.php
===================================================================
--- wp-includes/update.php	(revision 31266)
+++ wp-includes/update.php	(working copy)
@@ -21,7 +21,7 @@
  * @return null|false Returns null if update is unsupported. Returns false if check is too soon.
  */
 function wp_version_check( $extra_stats = array(), $force_check = false ) {
-	if ( defined('WP_INSTALLING') )
+	if ( defined('WP_INSTALLING') || !apply_filters('check_update_core', true ) )
 		return;
 
 	global $wpdb, $wp_local_package;
@@ -185,7 +185,7 @@
 function wp_update_plugins( $extra_stats = array() ) {
 	include( ABSPATH . WPINC . '/version.php' ); // include an unmodified $wp_version
 
-	if ( defined('WP_INSTALLING') )
+	if ( defined('WP_INSTALLING') || !apply_filters('check_update_plugin', true ) )
 		return false;
 
 	// If running blog-side, bail unless we've not checked in the last 12 hours
@@ -339,7 +339,7 @@
 function wp_update_themes( $extra_stats = array() ) {
 	include( ABSPATH . WPINC . '/version.php' ); // include an unmodified $wp_version
 
-	if ( defined( 'WP_INSTALLING' ) )
+	if ( defined( 'WP_INSTALLING' ) || !apply_filters('check_update_theme', true ) )
 		return false;
 
 	$installed_themes = wp_get_themes();