You should listen to the podcast for details but the gist of it is that &quot;The Objective-C model of object-oriented programming is based on message passing to object instances. In Objective-C one does not call a method; one sends a message.&quot; So let&#x27;s say you have an app that uses a runtime. The runtime in turn may use private&#x2F;internal calls that your app is not supposed to use. Well there is no reliable way to prevent it because as long as you can construct a message and know the string&#x2F;name of the target you can call it and there is no easy way for static analysis to detect such behavior.<p>Some apps were exploiting this to get a list of running apps and things like that.