[driax]

They aren't confidential, at least not more than your full name. It's a common myth, probably stemming from the fact that there's plenty of laws about how to treat information that can be used to identify people. But those laws pretty much also applies if you just a have list of peoples full name.

Edit: Reading through the law, they are more confidential than your full name, though not by much. Generally you can't publish them publicly. And usage within companies and the state are regulated, but fairly permissive. Datatilsynet has explicitly said that they shouldn't be used to identity that a person is who they say they are, and only should be used as a primary key to differentiate people.