Ken Xie had already built and sold one firewall company when he started his second. NetScreen, his first, went to Juniper. With Fortinet he and his brother Michael bet that companies were tired of buying a separate device for every kind of threat. Their FortiGate boxes ran on custom chips and packed many defenses into one appliance. Fortinet filed to go public in 2009, when the IPO market had barely woken up from the financial crisis.

Two Brothers, Custom Chips

The Xie brothers founded Fortinet in 2000 in Silicon Valley. Most security vendors ran their software on general-purpose processors. Fortinet designed its own chips to speed up the heavy work of scanning traffic. That let one FortiGate handle firewall, antivirus, VPN, and intrusion prevention at once without slowing the network. The pitch suited small and midsize businesses that had no big security team. Fortinet also sold to carriers and large enterprises.

Priced Above the Range

Fortinet priced its IPO at $12.50 a share in November 2009, above its planned range of $9 to $11. It raised $156 million and was the first security IPO since 2007. The stock rose about 33 percent on its first day on Nasdaq. Fortinet kept growing through the next decade as firewalls moved into cloud and remote work. Ken Xie still runs the company as CEO, and it trades on Nasdaq as FTNT.

Cover: Siege of the Citadel of Saint Martin on the Isle de Ré, Jacques Callot. Art Institute of Chicago, public domain. Chosen for a besieged island citadel (fortified defense).