We've been around the block a time or two.

History in tech

A timeline of important events since the dawn of cybersecurity, and some of our team's contributions across the years.


November 9, 1988

Robert Morris Jr. Internet worm unleashes fury on the world — Rule4 co-founder participates in forensic investigation. This is the dawn of Internet cybersecurity.

July 1, 1989

“UNIX System Administration Handbook,” 1st edition is published — a Rule4 co-founder is a collaborator and technical reviewer.

September 1, 1989

A team from University of Colorado Boulder (including a Rule4 co-founder) installs a network for the Princeton University Computer Science Building, the first purpose-built computer science building in the U.S. with high-speed networking to every desktop.



Rule4 co-founder rewrites parts of popular UNIX/Linux tool sudo. See more about the History of Sudo.

January 1991

Berkeley Software Design, Inc. (BSDI) is founded, including a Rule4 co-founder. Mission: Make the first fully commercial, non-AT&T UNIX.

January 1991

XOR, Inc. is founded by Rule4 co-founder.


Colorado SuperNet (non-profit) contracts with XOR to establish local dial-up Internet in all Colorado calling areas.



Rule4 co-founder discovers a hacker in Colorado SuperNet systems; this discovery eventually leads to the arrest and conviction of now-famous industry evangelist Kevin Mitnick.


BSDI, including a Rule4 co-founder, and The Regents of the University of California are sued by AT&T Unix System Laboratories for intellectual property issues stemming from alleged use of licensed UNIX source code. Learn More


Rule4 co-founder enters Ph.D. computer science program at CU Boulder focused on distributed systems and machine learning.


Rule4 co-founders establish community cooperative non-profit Internet provider, Colorado Internet COOP. Becomes largest commercial Internet-bandwidth provider in Colorado (for a time).


AT&T/BSDI/UCB lawsuit is settled favorably, but BSDI and BSD UNIX are mortally wounded. Linux has stepped into the void created by AT&T hugging its child to death.


XOR launches first real-time Internet rental car booking system (alamo.com) against claims that it “couldn’t be done.” Saves Alamo from the brink of bankruptcy and ignites the Internet as the way to book travel.


XOR designs and produces first enterprise monitoring platform olympics at Enterprise Management Summit in Dallas, Texas.


“Unix System Administration Handbook,” 2nd edition is released. A Rule4 co-founder is a primary author.

November 17, 1997

A legend is born: qwest.com domain is first registered by one of Rule4’s current leaders. Qwest goes on to swallow Baby Bell (RBOC) US West in 2000.


XOR launches wholefoods.com, the online home of Whole Foods Market, and the first Internet full-service holistic foods purveyor.


XOR is acquired by a Chicago private-equity firm, acquires multiple other web consulting firms to become one of the largest e-commerce powerhouses in the U.S.


“UNIX System Administration Handbook,” 3rd edition is released.


Founding of AppliedTrust, one of the first dedicated cybersecurity consultancies. “You’ll never be able to find enough security business,” said one mentor.


XOR is acquired by credit-scoring firm FICO.


“Linux Administration Handbook,” 1st edition is released.


“Linux Administration Handbook,” 2nd edition is released.


AppliedTrust wins coveted Colorado Technology Association APEX Award as Service Company of the Year.


“Unix and Linux System Administration Handbook,” 4th edition is released.


Rule4 co-founders create “Boulder Is for Startups” campaign acknowledging Boulder’s growing tech dominance.


Rule4 co-founder Dan Mackin is named Chief Operating Officer of AppliedTrust.


AppliedTrust is acquired by industry-leader ViaWest.


ViaWest + AppliedTrust is acquired by Peak10 and changes name to Flexential but remains in technology/datacenter industry.


“Unix and Linux System Administration Handbook,” 5th edition is released, includes two co-founders of Rule4 as primary authors.


Rule4 becomes a
Certified B Corporation.

Sept. 2020

Boulder County names Rule4 one of its “core partners” in an election security community briefing ahead of the 2020 presidential election.


Rule4 wins Startup of the Year award at Boulder Chamber’s Celebration of Leadership.


Rule4 is authorized as a Registered Provider Organization (RPO) by the Cybersecurity Maturity Model Certification Accreditation Body (CMMC-AB).

Feb. 2021

Rule4 Co-CEO Dan Mackin is chosen as CEO of the Year by the Colorado Technology Association.

Oct. 2021

Out of 1,100 nominations, Rule4 is chosen as one of 50 Colorado Companies to Watch.

Nov. 2021

Rule4 is ranked #4 on Outside’s list of the 50 Best Places to Work in 2021.

Nov. 2022

Rule4 makes Top 10 of Outside’s 50 Best Places to Work list for second straight year.

Feb. 2023

The Colorado Technology Association names Rule4 the Emerging Tech Company of the Year.

Feb. 2023

Rule4 SVP of Operations wins the Emerging Leader of the Year Award at Colorado Technology Association Summit.

Jan. 2023

Rule4 named to prestigious tech industry list of best places to work.

Aug. 15, 2023

In its first year of eligibility, Rule4 is ranked #2,990 on the prestigious Inc. 5000.

Nov. 16, 2023

Rule4 is ranked #1 on Outside Magazine’s list of Best Places to Work in 2023.