--- includes/bootstrap.inc
+++ includes/bootstrap.inc
@@ -523,8 +523,11 @@
       }
 
       // Send appropriate response:
+      header("Expires: Sun, 19 Nov 1978 05:00:00 GMT");
       header("Last-Modified: $date");
-      header("ETag: $etag");
+      header("Cache-Control: no-store, no-cache, must-revalidate");
+      header("Cache-Control: post-check=0, pre-check=0", false);
+      header("Pragma: no-cache");
 
       // Determine if the browser accepts gzipped data.
       if (@strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') === false && function_exists('gzencode')) {