/**
  * Create and return a hash for the download link.
  *
  * @return string The requested hash
  */
 public function serialz()
 {
     // encrypt the hash for the download link
     return Mage::helper('core')->getEncryptor()->encrypt(microtime() . $this->_linkPurchased->getCustomerId() . $this->_linkPurchased->getProductId() . $this->_linkPurchased->getPurchasedId());
 }