I have created custom attribute "CustomerAccount".Customer does not have access to this field .When new customer account is created CustomerAccount field should get random unique value and should get save in customer module.
You can use this extension for creating customer attributes. http://www.magentocommerce.com/magento-connect/customer-attributes-manager-5092.html
and if you don't want to show them on front end you can modify saveAction() function of its indexcontroller.php where it decided where to show attributes. It can work with magento 1.7 CE