Cyberspace, the combination of computer systems, devices, and the networks that connect them, is pervasive. However, from a security perspective, the invisible nature of cyberspace creates an issue-people have no intuition about how it works, and so cannot easily judge which actions are potentially dangerous. It's hard to assess the risk of any particular action in cyberspace, and many of the "rules" come without explanation, or least without meaningful explanation, that would enable users to understand when rules have reasonable exceptions. Education about cyberspace can help, and that's the purpose of this book, but a little learning is a dangerous thing. Browsers and servers developed new functionality, Servers no longer simply provided content, but enabled interaction with users, including allowing users to upload content. Although the Internet stretches into every country on earth, national governments have little control over it.