The biggest risk doing this on a botnet that I can see is that there's a chance some researcher looks at what you're doing and alarms the world before you get a

The biggest risk doing this on a botnet that I can see is that there's a chance some researcher looks at what you're doing and alarms the world before you get a result. There's no big risk of that on EC2. Using a botnet for compute has opportunity cost attached to it. However, I have no idea about the usual prices when they are rented.