How to Share your Internet Connection Safely

Suppose one of your guests or a juvenile visitor wishes to share your Internet connection. You could let them do that with your WiFi (or wired) network. There could be serious problems in doing that though.

The problem

Windows grants "trusted" status to all the computers that are connected to the same router. If any one of them is infected with malware, the rest of them are likely to be infected too. That's because the defenses that Windows maintains against intrusion from the Internet are dropped for computers on the local area network (LAN).

Beyond vulnerability to malware, there's also the questions of snooping or tampering. It's very easy to access one computer from another on a LAN; that's what networks are for.

The solution

First a little background: Routers provide a natural barrier to intrusion through their Internet side. It's a side effect of network address translation. The router only passes packets to the computer that requested them. It rejects unsolicited ones. Most modern routers also have a built-in firewall. The result is that computers on the LAN side of a router are very well buffered from nastiness on the input side of the router.

If you have set up a WiFi (or wired) network, you already have a router. All you need to do is separate your computer(s) from your guest's computer by another router, as shown in the figure from Ask Leo.

Similar to the way Leo explains it, Router A put's the kids computers on a one-hop extension of the Internet. Router B still sees the Internet in much the same way. It has been expanded by a few computers, but there are millions if not billions of computers on the Internet already. ;-)

Router B protects your own computer(s) from the Internet as well as the LAN created by Router A. An untrusted computer connected to Router A can access Router B, but if you've changed the administrative password for Router B, it will be very difficult for malware or user on untrusted computer to tunnel through Router B to access one of your computers.

One final note

As we've seen, Windows does very little to protect the computers connected the same router from each other. It's important to provide that protection by installing an effective security system on each one of them.