2. The Locked Front Door

As soon as your network connects to somewhere outside your building, you need the virtual equivalent of a locked front door. If you don't have that, all the information you have on your computers is vulnerable to anyone who wants to gain access.

Like real doors, virtual doors come in a wide variety of types, security levels, and expense.

The simplest, but not the safest, way to secure your network is to keep 'moving' - if you're connected to the internet through a modem and have a 'dynamic IP address' (ask your service provider), your address keeps changing. If your address keeps changing, and you're never on the internet for very long, it's very hard for someone to deliberately intrude on you. However, many computer intruders are like teenagers - they will go to great lengths for what they perceive as 'fun'. I recommend at least some security beyond this, even if all you ever do is read and write email.

As soon as you have a stable address and a permanent connection, you lose the 'obscurity' advantage that a dynamic IP and sporadic connection provides. You must install a real 'front door'.