Coming back to the topic of computer security, the TCP Wrapper is an example of such a safety net. I wrote it when my systems were under attack by someone who appeared to walk through walls.
-- Wietse Venema
   
Wietse Venema   Name:
Wietse Venema
Type:
Scientist
Nationality:
Dutch
Birth:
1951
https://www.nutquote.com/quote/Wietse_Venema