The law needs to be at the same standard as real life. For example the police can search your belongings unless they're locked, then you need a warrant. If you've got a service wide open on the internet with no security it shouldn't be a crime just because somebody found it.
The difference between doors and locks is that going through real life doorways is a lot different than connecting to a service. On the internet the act of connecting to it gives you access to the inside, there's no second act of walking in.
It's like an open door that throws a copy of it's contents at anyone that finds it.