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to target or manipulate them for information or access. Reducing static patterns in personnel taskings and changing access roles repeatedly reduces the opportunity for external actors to subvert particular employees as targets.

      Finally, job rotation also greatly improves the resiliency of an organization, essential in successfully executing BCDR actions. During contingency events or disasters, you must assume that some personnel will not be available/capable of performing particular tasks and functions necessary to maintain the organization's critical processes; having other personnel not normally assigned to those functions but trained on how to perform them is a great benefit and vastly increases the likelihood of BCDR response success.

DOCUMENT, IMPLEMENT, AND MAINTAIN FUNCTIONAL SECURITY CONTROLS

      Functional security controls implement the risk mitigation decisions that management and leadership have endorsed. The risk assessment and vulnerabilities assessment tasks have led to these decisions; now it's time to make appropriate cost-effective choices about particular controls, thus operationalizing those decisions by providing the tools, techniques, systems elements, and procedural step-by-step that the organization's workforce will need as they go about their day-to-day activities.

      The organization has already made decisions about which risks to avoid (by not doing business in particular locations or by abandoning particular business processes); it's also recognized some risks must just be accepted as they are, as an unavoidable but still potential cost of doing business. Chapter 3, “Risk Identification, Monitoring, and Analysis” goes into further depth on how information risks are identified and assessed and how organizational leadership makes both strategic, big-picture risk management decisions, as well as planning for risk mitigation and making the resources available to carry out those plans. Management has also transferred what risks it can to other third parties to deal with. What's left are the risks that you and the rest of your organization's security professionals must deal with. You deal with risk using five basic types of controls: deterrent, preventative, detective, corrective, and compensating. Note that there are no hard and fast boundary lines between these types—a fence around the property both deters and prevents attackers from attempting to cross the fence line, while a network intrusion prevention system both detects and attempts to block (or prevent) intrusions on your networks.

      Note that this section focuses on security controls, which are of course a subset of the larger problem of risk mitigation. From a security controls perspective, you think about these controls as interfering with a human attacker (or their software and hardware minions) who is carrying out an unauthorized intrusion into your information systems or causing damage or disruption to those systems.

      Let's take a closer look at each type of control and then examine common issues involved with their implementation, maintenance, and operational use.

      Deterrent Controls

      Deterrent controls work to dissuade an attacker from initiating or continuing in their efforts to attack your systems, property, information, or people. Their design, deployment, and use should all raise either the perceived costs or risks to an attacker and the actual costs the attacker could face should they choose to persist. Guard dogs off of the leash, free to range around your property (but within a fence line), are an example of a deterrent that offers painful costs to an attacker, while raising the probability of being forcibly detained and subjected to arrest and prosecution as well.

Deterrent controls should provide a variety of capabilities to the security architect by placing barriers (real and perceived) between potential attackers and the systems they defend.

       Visible, tangible barriers, which an attacker can see, sense, or probe, signal that the target is defended.

       This suggests that the barriers are alarmed and monitored, which increases the possibility of an intrusion being detected.

       The barriers suggest to the attacker that greater assets, time, or effort must be expended for their attack to succeed.

       They also suggest that more barriers may be encountered, layer upon layer, should the attacker continue in their attempt.

      Note the key concept that to be effective, a deterrent control must be visible, observable, and verifiably present to the prospective intruder. It cannot deter an attacker if the attacker doesn't know that it is there! This directly suggests that you're defending against a known group of attackers and that you have some degree of operational threat intelligence data, which you can use in selecting potentially effective deterrent tactics and techniques.

      Simple deterrents can be physical controls, such as fences, locked doors and windows, or landscaping and paving that restricts the movement of vehicles and pedestrians onto a protected property or campus. Exterior lighting, including the use of moving spotlights or floodlights, can also provide a deterrent effect. Most physical controls are passive, in that they do not react to an intrusion attempt; active controls would include guard dogs and security controls, for example.

      Physically, the architecture of buildings or workspaces make statements about an organization and the work that is performed there. These statements can also be powerful deterrents to would-be attackers. Think about how many modern embassy compounds (and not just the American ones) around the world have been transformed into little fortresses as they've been blast-hardened, surrounded by impact-resisting barrier walls, and armed military personnel or security guards; entry onto such embassy grounds is restricted and tightly controlled in most cases. High technology companies have also made similar architectural deterrent statements with the ways that they design, build, and operate their physical locations. These are definitely not statements of security through obscurity.

Network systems such as firewalls and intrusion detection and prevention systems can act as powerful deterrents by thwarting an attacker's ability to gain meaningful insight via reconnaissance probes or scans. (It's somewhat unfortunate that the line between NIDS and NIPS as product systems has become quite blurred at this point since both apply filtering rules of varying potency to block or restrict traffic from crossing their point of protection.) Well-trained, highly aware people throughout your organization are also effective deterrents when they smoothly deflect social engineering attack attempts, perhaps by guiding unknown callers through a well-rehearsed script to filter out the innocent prospective customer, client, or job seeker from the whaler-wannabee.

      Preventative Controls

      Preventative (or prevention) controls provide two forms of protection to keep your systems from harm by reducing the probability of an occurrence of a risk or, when it starts to occur, by containing it in such a way as to limit the spread of its disruption or damage. Securely locked doors and windows prevent an intruder from unlawfully entering your home, unless they want to elevate their risk by breaking through the locks, the windows, or the doors in question. The design of interior walls, doors, and utility spaces restricts the speed with which fire can spread from room to room, while reducing or blocking the spread of smoke and heat. This suggests that security architects should use prevention (like deterrence) in layers.

      Prevention can be active or passive, as with deterrence; the same types of controls used for physical, passive deterrence also bring some prevention with them.

      Host-based or network-based firewalls, intrusion detection and prevention systems, and of course identity management and access control systems are the main components of a solid prevention architecture. Layer upon layer, they detect attempts to cross a threat boundary's controlled access points; they test that access attempt against varying sets of criteria and in some cases issue challenges requesting further credentials from the requesting subject. Since all of these systems can and should generate both accounting log information for successfully authenticated attempts, and alerts or alarms for failures, they are deterrent, prevention, and detection systems all at the same time.

      Detective

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