protected function _isDuplicate($params)
    {
        $pspReference = trim($params->getData('pspReference'));
        $success = trim($params->getData('success'));
        $eventCode = trim($params->getData('eventCode'));

        // if notification is already processed ignore it
        $isDuplicate = Mage::getModel('adyen/event')
            ->isDuplicate($pspReference, $eventCode, $success);
        if ($isDuplicate && $eventCode != Adyen_Payment_Model_Event::ADYEN_EVENT_RECURRING_CONTRACT) {
            return true;
        }

        return false;
    }