Let’s start with a question. In the face of modern adversaries, can a system be deemed secure if it uses the latest technology at the edge? Fundamentally, there are a couple of issues in this question. First, there are no “perfectly” safe systems, only safer ones. Second, security is not about protecting the perimeters anymore; attackers are looking for gaps in our design from all directions.

Defense in Depth is a security design principle that layers security controls to protect, acknowledges the inevitability of failures, and focuses on resilience to create a formidable barrier against the modern threat landscape. Recent attacks such as the SolarWinds attack taught us that protecting the interfaces of a system is not enough; security needs to be part of every phase of the software development life cycle. If we break down security practices in organizations, they can be broadly categorized as follows:

• Application or product security, sometimes platform security
• Enterprise, corporate, and infrastructure security
• Security governance, policy, and compliance

There are plenty of good resources that cover these topics individually. However, successfully designing, building, and maintaining robust security systems is much more complex than a random mix of these pillars. As attackers grow ever more sophisticated, using AI and automated tools, Defense in Depth provides a structured, proactive framework for building resilient systems designed to withstand the onslaught.

As we become more reliant on the digital ecosystem, security by default will become increasingly relevant. To be able to secure software against advanced cyber threats, one needs a holistic understanding of the individual pieces and their interplay. In this book, I aim to provide a comprehensive overview deeply rooted in security-first principles. I will guide you through real-world attacks to help you build a mental map and a framework that can withstand advanced threats.

Defense in Depth is in the spotlight in every critical security role today. The escalating frequency and sophistication of cyberattacks are only going to drive the surge. High-profile breaches have exposed the futility of relying solely on prevention. Defense in Depth acknowledges this, providing a practical framework for resilience. It emphasizes layered protection, continuous monitoring, and strategies to limit the damage caused by successful attacks.

As demands grow, Defense in Depth is going to be a crucial skill for every security professional and it will have faster growth opportunities.