Consider public internet address to be insecure
When the user's computer is connected directly to the internet (through a cable modem for example), or some other bridged network, we should check the IP address, and disable shares if the IP is not a private one.
The following ranges are reserved by the Internet Assigned Numbers Authority (IANA) for use as private IPv4 addresses: 10.0.0.0 to 10.255.255.255. 172.16.0.0 to 172.31.255.255