Good day,
How are you?
The bad thing about a botnet, is legitimate customers can be part of it. Do you have your customers register before submitting an order?
If you want anonymous orders, might want to setup external payment gateways like Paypal, DevPay and Google Checkout because they filter bad countries, users, etc.
I've been setting up eCommerce sites since the 1990s, so I've seen it all, protected against these types of issues and helped the purchasing workflow to benefit the company.
Let me know if you have any questions.
Sincerely,
John