Most information that will be of vital interest is protected and you need a certain level of authentication to get it. To see all the files on a computer you need super-user privileges—a user account that is given the same privileges as the "root" user in Linux and BSD operating systems. For routers this is the "admin" account by default (unless it has been changed); for Windows, this is the Administrator account. There are a few tricks you can use to gain super-user privileges:
Buffer Overflow: If you know the memory layout of a system, you can feed it input the buffer cannot store. You can overwrite the code stored in the memory with your code and take control of the system. 
In Unix-like systems, this will happen if the bugged software has setUID bit set to store file permissions. The program will be executed as a different user (super-user for example).

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