Index: modules/taxonomy/taxonomy.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/taxonomy/taxonomy.module,v
retrieving revision 1.425
diff -u -r1.425 taxonomy.module
--- modules/taxonomy/taxonomy.module	24 Jul 2008 16:25:19 -0000	1.425
+++ modules/taxonomy/taxonomy.module	26 Aug 2008 12:27:34 -0000
@@ -1131,6 +1131,8 @@
     $output .= theme('pager', NULL, variable_get('default_nodes_main', 10), 0);
   }
   else {
+    // Remove (outdated) categories without content from search engines.
+    drupal_set_header('HTTP/1.1 404 Not Found');    
     $output .= '<p>' . t('There are currently no posts in this category.') . '</p>';
   }
   return $output;