Who We Are

We operate at the intersection of artificial intelligence and cybersecurity, developing solutions that merge the depth of human reasoning with the scalability and precision of AI

Our Story

Off By One began with a focus on making real-world security expertise accessible to the broader cybersecurity community. Founded by Stephen Sims, the Off By One Security channel centered on intermediate and advanced topics that were often missing from public training and discussion. The goal was to create a space where practitioners could learn from experience, not just theory.

That effort evolved into a company built to address the growing gap between how attacks are carried out and how organizations test their defenses. After decades working in penetration testing, red team operations, and vulnerability research, Stephen and Huascar Tejeda saw an opportunity to apply emerging advances in AI to persistent challenges in security testing. Off By One Security was formed to leverage expert knowledge for scalable solutions, combining human insight with intelligent automation to help organizations better understand risk across modern applications.

Our Purpose

To advance offensive cybersecurity through a balance of human expertise, real-world exploitation, and intelligent automation.

Our goal is to give every organization, from startups to global enterprises, the ability to test, discover vulnerabilities, and strengthen their defenses, at scale, with the same precision as the most technical offensive security professionals.

Our Mission

Close the gap between how attackers evolve and how defenders respond.

Off By One delivers a unified suite of offensive security solutions, from AI-powered platforms to deeply technical testing services, that help organizations understand and improve their security posture. Whether through advanced pentesting engagements or intelligent automation, we make proactive security achievable for organizations.

Our Approach

Off By One blends decades of frontline expertise with cutting-edge research in artificial intelligence.

ACID is trained with a deep understanding of how attackers think and how defenders operate. By automating human reasoning with AI technologies, we bridge the gap between manual testing and machine-driven discovery.

Our Vision

We envision a cybersecurity ecosystem where humans and AI collaborate seamlessly to outpace threats. Through our innovative platform and expert-led services, Off By One aims to redefine speed to security.

Who We Serve

We work with organizations and teams responsible for securing modern applications, APIs, and AI-driven systems. Our solutions are built for environments where scale, complexity, and real-world risk demand more than periodic testing.

We serve teams and organizations including:

Application and Product Security Teams
Securing web applications and APIs that change frequently and require continuous testing beyond manual coverage.
Development and Engineering Teams
Building and deploying software at speed who need security insight integrated into workflows without slowing delivery.
Red Teams and Internal Security Groups
Testing defenses using realistic attack techniques and repeatable methodologies to measure detection and response readiness.
Security Consultancies and Boutique Firms
Delivering high-throughput testing, consistent reporting, and scalable methodologies across multiple client environments.
Organizations with Large API Ecosystems
Managing complex, interconnected APIs where authorization flaws, logic errors, and data exposure present elevated risk.
Companies Deploying AI and Chatbot Capabilities
Securing LLM-powered interfaces, agent workflows, and AI-driven features exposed to users and external systems.
Highly Regulated Enterprises
Operating in sectors such as financial services, healthcare, and government where security assurance and audit readiness are critical.

Our Team

Stephen Sims – Founder, CEO

Stephen Sims is a recognized leader in security research, testing, and education with decades of experience working at the cutting edge of offensive security. His career spans deeply technical vulnerability research, curriculum development, and teaching advanced techniques to practitioners worldwide. Stephen founded Off By One to translate that experience into practical solutions that raise the bar for how security testing and training are delivered.

SANS Institute Fellow and Curriculum Lead for Offensive Operations
Co-author of the Gray Hat Hacking book series
International speaker at major conferences including DEF CON, OWASP AppSec, and RSA keynotes

Huascar Tejeda – Founder, CTO

Huascar Tejeda is an accomplished security researcher and technologist known for solving complex problems across applications, infrastructure, and embedded systems. As the founder of Pentraze Cybersecurity, he has led advanced testing engagements for organizations operating in high-risk environments. At Off By One, Huascar drives the technical direction, turning real-world attacker knowledge into intelligent platforms and scalable testing capabilities.

Co-author of the Gray Hat Hacking book series
Founder of Pentraze Cybersecurity
Widely recognized vulnerability researcher and competitive CTF champion