Oh damn, I am new to shopify, but I have a site on Magento where I have card attacks that would literally run tens of thousands of card attempts within an hour. hundreds per second. But in magento I used Braintree as a processor and I… (1) I used AVS and declined any transaction that the address did not match the credit card billing address. (2) I set a few fraud rules “Reject when 5 or more transactions have the same customer ID within 30 minutes” and “Reject when 5 or more transactions have the same credit card number within 30 minutes”.
That prevented any successful transactions but that card attack still shut my site down while it was going on because it was just too many transactions. and the processor wrote me. I then put up a google recaptcha on the checkout page. We will see how that goes.
But I just launched a site here on Shopify. It seems crazy that there is no way to prevent that. I adding to this post in hopes that if there is ever some tool to prevent card attacks, that I will be notified also.