.NET How to Stop a user from deleting the file?

I got this exam question "How to Stop a user from deleting the file?" I assume I should use some permission attribute, but which?

Use FileInfo and set its .IsReadOnly property.

        Dim fi As New FileInfo("c:\temp\temp.txt")
        fi.IsReadOnly = value

You cannot prevent a user with administrative rights from deleting a file. After all, he can overtake the file's ownership and change the permissions.