Nir Zuk had already built firewalls at Check Point and NetScreen when he decided they were looking at the wrong thing. Old firewalls checked ports and addresses. By the mid-2000s, apps slipped through any open door. Zuk founded Palo Alto Networks to build a firewall that knew which app was behind the traffic. When it filed to go public in 2012, it was the fastest-growing name in network security.

Three Firewalls In

Zuk founded Palo Alto Networks in 2005. He had worked as an engineer at Check Point in the 1990s. He then co-founded OneSecure, which NetScreen bought in 2002, and served as NetScreen's chief technology officer. His bet was that a firewall should see apps, users, and content. That let a company allow one app and block another on the same port. Big companies began to swap out their old boxes.

A Watchtower on Wall Street

Palo Alto Networks priced its offering at $42 a share on July 19, 2012. The stock rose 26.5 percent on its first day on the New York Stock Exchange and closed at $53.13. The company then spread from firewalls into cloud security and security operations. It moved its listing to Nasdaq in 2021. Palo Alto Networks still trades there as PANW.

Cover: The Lonely Tower, Samuel Palmer. Art Institute of Chicago, public domain. Chosen for a lone watchtower (guarding the network).