The second layer of security deals with file access security. At this level, the user can
create a file and establish various combinations of individuals to have access to it
because the operating system makes distinctions between owners and groups. The creator
of a file is its owner. The owner can designate a set of users as belonging to a
group and allow all the members of the group to have access to that file. Conversely,
the owner could prevent some of the members from accessing that file.