"It's peer-to-peer, trust me bro!" The problem is that you are still using a website provided by a third-party to serve you the JavaScript program that initiates the transfer. It's easy to replace that JavaScript by something that just transfers a copy to the third-party itself. To be sure that the transfer is actually peer-to-peer, either the sender or receiver should run their own fillepizza server (and have verified that the source code does not contain any backdoors or phone-home code). But if you do that, you actually don't need a peer-to-peer solution anymore, it's turned into a client-server problem.