The court held that the combination of (a) using Limewire, (b) configuring iTunes folder for sharing, and (c) operating an unsecured wireless network eliminated the need for a deputy sheriff to get a warrant to access the shared file via the network to find child pornography.
I think this is correct. True, as defendant argued, people are ignorant and rely on the defaults, which are open. Tough. When you leave your system utterly open in this fashion, there are two possible conclusions for the innocent third party: either you intend to leave the system open for sharing, or you are unaware you have left the system open. As the system is entirely in control of the owner, and there is no easy way to signal "I meant to leave this open," it seems reasonable to me to say "if something is wide open, assume the invitation. In the real world, we would judge whether an open door is an invitation or not by the context. In the digital world, the context has long been that leaving everything open is an invitation to share the resource.