From the quick look, digital download protection based on IP address and storing files in Dropbox? That makes me uncomfortable and I see tons of potential issues here.
Also what does automatic fraudulent payment detection involves?
My system keeps track of failed payment attempts (e.g. a declined credit card OR invalid card code). When a successful payment is made, I look through the history of failed payments to look for patterns that can determine a possible fraudulent transaction. An example of a pattern would be an IP address that tried to use X number of credit cards over the past X hours.