It's "private" in the sense that it's not going over the public network, rather than private to your account. This was pretty clear when the feature was announc

It's "private" in the sense that it's not going over the public network, rather than private to your account. This was pretty clear when the feature was announced. I don't know why it's a surprise now. You still have to secure your server, even if it's only communicating over the "private" interface. I usually use this feature for database servers, and lock down the firewall so that only the web servers can communicate with the db servers, and only via the "private" interface.