What does "defense in depth" refer to in network security?

Defense in depth refers to a comprehensive security strategy that employs multiple layers of security controls across various points in a network. This approach recognizes that no single security measure is foolproof or sufficient on its own, hence layering different types of security mechanisms creates redundancy and enhances overall protection.

By implementing a strategy with multiple security controls, organizations can better mitigate risks and defend against a variety of threats. For instance, layers might include firewalls, intrusion detection systems, antivirus software, and user training programs among others, all working together to create a robust security posture.

Other options do not encapsulate the essence of defense in depth. A single-layer security approach fails to provide the multi-faceted defense necessary for effective protection. Software applications for threat detection are crucial tools but do not represent the overarching strategy of layering defenses. Similarly, while user training enhances security awareness, it is just one component of a broader defense strategy and does not encompass the full scope of defense in depth.