In this section, you'll learn the exact opposite of what we've done throughout this book when it comes to network security. We are going to make the Pi available to the big bad Internet, and not only on your local network.

There are plenty of reasons why one would like to do this. Perhaps you'd like to log in to your Pi from work, school or from an Internet cafe around the globe. Maybe you'd like to run your own instant messaging service for only yourself and your group of friends.

There's absolutely nothing wrong with these goals, as long as you understand that there are certain risks associated with inviting outside traffic inside your home network. As we speak, there are thousands of automated attacks running wild on the Internet, scanning for badly configured services and vulnerable software to exploit for fun and profit.

If a malicious human or application manages to compromise your Pi, the best case scenario is that you notice it and...