Most probably your server is running on Linux™, or another UNIX™-derivative operating system. You might have read, or heard, how these operating systems are safer and more secure than others. This is just half the story. The real security power of such operating systems stems from the way they manage files and directories, allowing or disabling access to them depending on who asks for it and what he's trying to do.
This management is pretty much like electricity in the Western world. It never gets in your way and you don't think about it, but you must have some basic understanding of it so as not to run the risk of getting toasted by it. That's how it goes with ownership and permissions. You might not think about them a lot, but potentials crackers do. If you don't manage permissions wisely, you might be creating a security hole on your server which can be exploited by a malicious cracker. Nobody wants his site cracked, right?
The following chapter will analyze how your web server works under the hood, so that you can grasp the third chapter, which analyzes all the ways you can secure your backup files so as not to fall prey on a cracker.