Dangling symlinks

If you ran the following code

  open FH, ">dangling" or die;

The actual target of 'dangling' (nada) would be created, as long as the invoking user can do so.

Create .rhosts / .shosts files for normal users.
Allow passwordless login to their account.

Create /etc/nologin as root.
Deny everyone the ability to log in.