function anonymize_data_menu() {
  $items = array();
  $items['admin/config/content/anonymize-user-data'] = array(
    'title' => 'Anonymize User Data',
    'description' => 'Click this link to anonymize user data',
    'type' => MENU_LOCAL_ACTION,
    'page callback' => '_anonymize_users_data',
    'access arguments' => array('administer user anonymize'),
    'file' => 'anonymize_data.user.inc',
  );
  return $items;
}

function _anonymize_users_data() {
  $users = entity_load('user');
  $chunks = array_chunk($users, 20);
  $count_user = count($chunks);

  foreach ($chunks as $chunk) {
     $operations[] =  array('user_anonymize_op', array($chunk));
      //user_anonymize_op($chunk);
     //krumo($chunk);
  }
  $batch = array(
    'operations' => $operations,
    'title' => t('Import batch'),
    'init_message' => t('Initializing'),
    'error_message' => t('An error occurred'),
    'finished' => 'user_anonymize_op_finished'
  );
  batch_set($batch);
  batch_process('admin/people');
}

function user_anonymize_op($users, &$context) {
  foreach ($users as $user) {
    # code...
    //krumo($user);
   $context['message'] = t('processing user @user', array('@user' => $user->name));
    //
      if($user->uid != 0 && $user->uid != 1) {
      $user->name = $i . '-' . $user->name;
      $user->pass = user_hash_password('blah');
      user_save($user);
    }
  }
}

function user_anonymize_op_finished($success, $results, $operations) {
  if ($success) {
    $message = count($results) . ' processed.';
  }
  drupal_set_message(t($message));
}