Mac® Security Bible

20.1. What Can Network Scanning Reveal?

The extent of the information a hacker can learn about your network depends on several factors, including how many devices, of what types, and using which operating systems, are on the network; whether you use a NAT router; whether your computers are running firewall software and, if so, how the firewalls are configured; and whether the scan is being performed from inside your network or from the outside. However, in general, the following pieces of data about each device on your network — computers, routers, printers, iPhones, and so on — are potentially up for grabs:

• The device's (private and/or public) IP address

• The MAC address and manufacturer of the device

• Whether the device supports IPv4, IPv6, or both

• The date and time the device was last restarted

• The device's operating system (type and version)

• Which ports are open on the device and which are being filtered or blocked

• Which application is listening on each open port

For example, as I type this paragraph, I'm sitting in a library, using its Wi-Fi network, and a few moments ago, I performed a network scan as I describe ahead. I can see a half-dozen other patrons with laptops open, and I can tell just by looking which models some of them are. By cross-referencing what my eyes tell me with what my network scan tells me, I know that the guy over there with the beard and the headphones, with a white MacBook in front of him, has SMB file sharing turned on and is still using last week's version ...