That's a good observation. And come to think of it, I did think of a way to disallow this type of activity, but not entirely. Since the client app will run on

That's a good observation. And come to think of it, I did think of a way to disallow this type of activity, but not entirely. Since the client app will run on a smartphone, the person using the phone will have to reinstall the application many times so that he could intentionally subscribe again and again to an event. So I guess one thing to do would be to register the mobile user with his mobile phone's unique identifier and not allow him to subscribe again to a previously subscribed-to event. Otherwise he would just have to buy more phones, but I don't think that's a practical solution.