Index: modules/user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user.module,v
retrieving revision 1.454.2.21
diff -u -p -r1.454.2.21 user.module
--- modules/user.module	29 Nov 2005 20:14:29 -0000	1.454.2.21
+++ modules/user.module	19 Feb 2006 23:41:54 -0000
@@ -813,6 +813,10 @@ function user_login($edit = array(), $ms
 
       user_module_invoke('login', $edit, $user);
 
+      $old_session_id = session_id();
+      session_regenerate_id();
+      db_query("UPDATE {sessions} SET sid = '%s' WHERE sid = '%s'", session_id(), $old_session_id);
+
       // Redirect the user to the page he logged on from.
       drupal_goto();
     }