Index: wp-includes/update.php
===================================================================
--- wp-includes/update.php	(Revision 17501)
+++ wp-includes/update.php	(Arbeitskopie)
@@ -57,8 +57,25 @@
 	}
 
 	$local_package = isset( $wp_local_package )? $wp_local_package : '';
-	$url = "http://api.wordpress.org/core/version-check/1.5/?version=$wp_version&php=$php_version&locale=$locale&mysql=$mysql_version&local_package=$local_package&blogs=$num_blogs&users={$user_count['total_users']}&multisite_enabled=$multisite_enabled";
 
+	$update_data = array (
+		'version'           => $wp_version,
+		'php'               => $php_version,
+		'locale'            => $locale,
+		'mysql'             => $mysql_version,
+		'local_package'     => $local_package,
+		'blogs'             => $num_blogs,
+		'users'             => $user_count['total_users'],
+		'multisite_enabled' => $multisite_enabled
+	);
+	$update_data = apply_filters( 'update_core_data_send', $update_data );
+
+	$query_string = '';
+	foreach ( $update_data as $key => $value ) {
+		$query_string .= "$key=$value&";
+	}
+	$url = 'http://api.wordpress.org/core/version-check/1.5/?' . rtrim( $query_string, '&' );
+
 	$options = array(
 		'timeout' => ( ( defined('DOING_CRON') && DOING_CRON ) ? 30 : 3 ),
 		'user-agent' => 'WordPress/' . $wp_version . '; ' . home_url( '/' ),