Chapter 7. Classification and Event Tools: IDS, AV, and SEM

This chapter focuses on the development and use of event-based sensors such as intrusion detection systems (IDSes). These systems include passive sensors such as IDSes and most AVs, as well as active systems such as firewalls. Analytically, they all behave similarly—they analyze data and create events in response to that data. Event construction is what differentiates an IDS from a simple reporting sensor such as NetFlow. Simple sensors report everything they observe, while an IDS or other classifying sensor is configured to report only on specific phenomena that it infers from the data it observes.

Many analytic processes will eventually result in some form of IDS. For example, you might want to develop a system detecting abusive activity on a host. Using some of the math in Part III, you build up a model of abusive activity, create some thresholds, and raise an alert whenever there’s a threshold.

The problem is that these processes almost never work as intended. Operational IDS systems are very hard to implement properly. The problem is not detection; the problem is context and attribution. IDS systems are easily, and usually, configured into uselesness. Either they produce so many alarms that analysts ignore them, or they’re configured to produce so few alarms that they might as well not be there. Developing effective alarms requires understanding how IDSes are used operationally, how they fail as classifiers, and the ...

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