Making documentation files non-readable?

This what it says in the 6.6 manual:

Some administrators suggest making the documentation files, especially
CHANGELOG.txt, non-readable so that the exact version of Drupal you are
running is slightly more difficult to determine. If you wish to implement
this optional security measure, use the following command from a shell or
system prompt (while in the installation directory):

chmod a-r CHANGELOG.txt

Note that the example only affects CHANGELOG.txt. To completely hide
all documentation files from public view, repeat this command for each of
the Drupal documentation files in the installation directory, substituting the
name of each file for CHANGELOG.txt in the example.

1. How do I make the files "non-readable", is this method same as CHMOD, or is it this: http://drupal.org/node/202491 and different from CHMOD ?
2. It says do the same for "each of the drupal documentation files", which files is this referring to exactly and how many are there so I don't overdo/underdo it?
3. Do I make the files non-readable before or after instillation?