95264 Oscommerce User Field needed

There has been a lot of fraud on my oscommerce website this last few weeks and I want to get the clients Identification Number before he can buy from me. I have 2 methods that would work for me. 1. Get the users ID number upon registration. This will be very easy, as you only have to add an additional field to get the ID number. This should also be visible from the admin area when I click on a customer. The field must be set to required and must be a min and maximum length of 13 numbers. With this option all customers will have to give me their ID numbers. 2. With this option I will only collect their ID number when they choose to pay by Credit Card(Custom Payment Module that I use - not the default oscom Credit Card system). So when they register, I do not ask for ID number, only when paying with Credit Card. The credit Card details will then be emailed to me along with the customers order details. Once again the ID should be visible somewhere in the admin area. Please let me know which way you think is better and how long/much it will be to do the work. Thanks