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It's legal to port scan networks you don't own (from a US perspective), though logging in and/ or performing changes to the device are definitely not. As another person has mentioned, you will get a lot of abuse emails but there's nothing illegal about port scanning by itself.

Source: I run Shodan (http://www.shodanhq.com)

As someone who has scanned e.g. all of 24.0/8 from a work machine, you do get angry emails to abuse@<your-reverse-dns-name>. I don't think there are legal issues here -- these are all public services on the internet. But installing software like the author did is legally problematic.

It's almost always against the terms of your provider's AUP.

That's why you do the scanning from someone else's router. :-)

Replacing possible AUP-violation with definite felony.

Isn't some AUP violation a felony, because you're using a computer without authorisation?