In 1995, Farmer and Wietse Venema (a Dutch programmer and physicist) developed a second vulnerability scanner called the Security Administrator Tool for Analyzing Networks (SATAN).

Due to a misunderstanding of SATAN's capabilities, when it was first published, some network administrators and law enforcement personnel believed that hackers would use it to identify and break into vulnerable computers.

[2] However, contrary to popular opinion, SATAN did not function as an automatic hacking program that undermined network security.

He co-developed the Titan vulnerability scanner with Brad Powell and Matt Archibald, which they presented at the Large Installation System Administration Conference (LISA) in 1998.

[5] Farmer co-founded Elemental Security with Dayne Myers, and served as the corporation's chief technical officer.