--- a/plugins/yubikey/auth.php	Thu Feb 26 16:33:06 2009 -0500
+++ b/plugins/yubikey/auth.php	Sun Mar 01 20:41:17 2009 -0500
@@ -165,6 +165,13 @@
   // Do we need to have the password validated?
   if ( $do_validate_pass )
   {
+    if ( empty($userdata['password']) )
+    {
+      return array(
+          'mode' => 'error',
+          'error' => 'yubiauth_err_must_have_password'
+        );
+    }
     // Yes; return and let the login API continue
     return null;
   }