Disable WordPress updates (functions.php)

disable_core_updates.php

//Diasable Core Updates # 3.0+
add_filter( 'pre_site_transient_update_core', create_function( '$a', "return null;" ) );
wp_clear_scheduled_hook( 'wp_version_check' );

disable_plugin_updates.php

//Disable Plugin Updates #3.0+
remove_action( 'load-update-core.php', 'wp_update_plugins' );
add_filter( 'pre_site_transient_update_plugins', create_function( '$a', "return null;" ) );
wp_clear_scheduled_hook( 'wp_update_plugins' );

disable_theme_updates.php

//Disable Theme Updates # 3.0+
remove_action( 'load-update-core.php', 'wp_update_themes' );
add_filter( 'pre_site_transient_update_themes', create_function( '$a', "return null;" ) );
wp_clear_scheduled_hook( 'wp_update_themes' );