When using secure MQTT, or secure MQTT over WebSockets, we have to deal with certificates, which would take up a huge portion of this book on its own, leaving us with no time for prototyping. Knowing about possible security issues is important, but unless your project is used permanently, or you work on prototypes for clients that will be used in production, it is not worth the hassle of setting up and updating SSL certificates, which are a requirement for a secure connection. I don't want to advise you to be careless. You should not update your microwave to be controlled via MQTT or create a door lock that communicates over an unsecured MQTT connection. This would be extremely careless and could result in some serious damage.