Originally posted here by mohaughn
Ask the owner of the network what the network was intended for.

I'll use the often used analogy of door locks. Even though I'm tired of seeing this analoyg. We need a new comparison if you ask me...

If I leave my backdoor unlocked and you walk in you are still breaking and entering. It doesn't matter that I was not smart enough to lock the door in the first place. Nor can you blame the owner of the network as he does not control the actions of the criminal.

I see unsecured networks all of the time. Do I ever use them, no. Why not? Because I wouldn't want somebody else poking around in my network. It's a matter of ethics. Just because you can break the law doesn't mean that you should or have a right to.
Well, here's the problem: the law, if it forbids this type of activity, is pretty confused.

Not only did the network likely advertise its presence and services (via SSID broadcast), and not only was it entirely open despite the fact that it didn't have to be, but in order to log on to the network, someone's computer had to request services and credentials (namely, an IP address through DHCP, as well as a link), and the network had to grant them to him. And worse, it would appear that the owner of the network deliberately left it that way (though I don't think this is critically important).

A closer analogy than the one above would be that a sign is hung on the door that says "Come on in! Public welcome. Just turn the knob!"

Now, how do you distinguish legally between this and any other, implicitly allowed network access? Beats me. But if I were the defense attorney, I'd sure make the case that this network was specificaly configured to provide services to any member of the public who wanted them, just like most open access ports out there...