Im not sure if this is possible but have you considered making your own website and making it have the capablities too run the game only there? That aay youre not risking the download file getting spread like wildfire! Just a small minded suggestion but in a perfect world that seems optimal too me.
Viewing post in Goodbye Eternity's future comments
Also, games playable only online can still get pirated. DFD and others were originally only playable on the creators website and encrypted, but someone still cracked it. And it was a very clunky experience. While their latest game, Shale Hill Secrets, still uses a version of the same engine, its a vastly improved experience.