That open should fail, as you're trying to go to the parent directory of the root node. And the fundamental point is, the root node for serving documents is not the file system's root node, and there's no URL that would allow access to it (assuming a non-insane configuration). So put your password file at '/etc/secret/password.txt' or any other location outside the web server's document directory structure, and it will not be accessible by browsing, even if the path and file name is known.
in reply to Re^4: Removing malicious HTML entities (now with more questions!)
in thread Removing malicious HTML entities (now with more questions!)
There is no rule that requires any file to be directly accessible by URL. What can be accessed is controlled by the server configuration.