Hacker, hack, and hacking are terms that have become ubiquitous in the 21st century. You've probably heard about life hacks, business hacks, and so on. While these may be, in some sense of the word, forms of hacking, the traditional form of hacking we'll discuss in this book is computer hacking. Computer hacking is the art of using computer-based technologies in ways they were never intended to be used to get them to do something unanticipated.

Hacking has taken on many different names and forms throughout the years. In the late 20th century, a common form of hacking was known as phreaking, which abused weaknesses in analog phone systems. Computer hacking has been around for more than half a century and, over the past few decades, has become a pop culture sensation in Hollywood movies and on television shows. It's all over the news, almost daily. You hear about things such as the Equifax, NHS, and Home Depot data breaches all the time. If you're reading this book, you have made your first step toward better understanding this fringe form of engineering.

Now that we have a better idea of what a hacker is, let's explore the various classifications of hackers.