Which scenario illustrates an example of a layered defense?

A layered defense, often referred to as defense in depth, involves implementing multiple security measures in a way that even if one layer is compromised, additional layers still provide protection. The scenario that depicts this concept is that after an initial defense is breached, a different defense must be overcome. This illustrates how a breach does not lead to total compromise, as there is a second layer of defense that can continue to protect the system or data.

In this context, if an attacker bypasses the first line of defense—such as a firewall—there are additional security measures in place, like intrusion detection systems or anti-virus software, that serve as subsequent challenges for the attacker. This multi-layered approach ensures that the security of the system is not solely reliant on one measure, thus increasing the overall security posture against attacks.

The other scenarios presented do not adequately represent the concept of layered defenses. For example, preventing an attacker from exploiting vulnerabilities through multiple defenses is a valid security strategy, but it does not emphasize the sequential nature of layered defenses as effectively as the correct option. Additionally, the use of proxy networks by attackers, while a method to obscure their activities, does not illustrate the defensive measures employed by an organization to protect its assets.