[einpoklum]

As others suggest: Sjunet is not really "private", in the sense that you can bet that there are unsupervised machines connected to it via some of the legit machines (or via some of the comm. equipment), which are also connected to the rest of the Internet via another Ethernet or WiFi connection. These can in principle expose open ports for interested parties to act as they wish on the "private" network. And they do so despite the reassuring contract which Sjunet members sign.