Digital products and credit card theft

[eluser]johnwbaxter[/eluser]
I have a shop that sells digital goods. You pay your money, you can download your product instantly.

Trouble is, i have recently had a few people buy who have used cloned / stolen credit cards. The credit card is accepted by the payment processor and tells my shop that all is well, so the shop releases access to the product.

A few hours later the person who's credit card it is notifies the payment processor that the transaction was fraudulent and i refund their money, but obviously someone else has got my product that i can't get back or trace who has it.

I'm wondering if i should put a 10 (or more) hour delay between people paying and actually delivering their product. This would be a shame as i would like it to be available to the purchaser as soon as they have paid.

Does anyone have any experience of this or any advice they could slip my way?