Thanks for the reply Elvira, but I’m not having any problem replicating this. I simply add the wrong CVC and the a receipt is generated through Woocommerce saying that the item is paid for. Square does NOT take payment, and the customer is told that the payment has gone through.
Normally, the customer would have a fail at the wrong CVC and then redirected to a payment failed page.
I have no problem replicating this on a live system.
We are now starting an audit as we may well have lost hundreds, if not a thew thousand through this bug.