When I speak at conferences or on panels, I often discuss the concept of thinking about data transiting a network in terms of "Known Knowns", "Known Unknowns", and "Unknown Unknowns". This was a concept that Donald Rumsfeld spoke to during the Iraq war. It's a concept that is very relevant to the cyber security world, and specifically to network monitoring/network traffic analysis. Unfortunately, it's a very underutilized framework, but it can add great value to an organization's network monitoring approach.
"Known Knowns" are network traffic data that we understand well and can firmly identify. Members of this class of network traffic can be categorized as either benign or malicious. Detection methods here can be automated and don't require much human analyst labor on a continuing basis. Unfortunately, this is the class of network traffic that we as a community spend the bulk of our time on. Why do I use the term unfortunately? More on that later.
"Known unknowns" are network traffic data that we have detected, but are puzzled by. We don't have a good, solid understanding of how to categorize this class of network data. One would think that because of this, we should spend a decent amount of time trying to figure out what exactly this traffic is. After all, if we don't know what it is, it could be malicious, right? Unfortunately, not enough time is put into this class of network traffic, and as a result, most organizations remain puzzled and/or turn a blind eye to the known unknowns. Why don't we work harder here? We're too focused on the known knowns.
"Unknown unknowns" are network traffic data that we have not yet detected, and as a result, we aren't aware of what this class of network traffic is (or isn't) doing on our network. This is the class of network data that contains most of the large breaches (and thus most of the collateral damage), as well as most of the truly interesting network traffic. Finding this traffic takes a skilled analyst, good tools, the right data, and a structured, well-organized approach to network monitoring. Ironically, this class would be extremely interesting to a skilled analyst, but due to the known known "rut" that we as a community are in, analysts don't really get a chance to touch this class.
So now I think you can understand why I think it's unfortunate that we as a community are so focused on the known knowns. We are so busy "detecting" that which we've detected time and time again, that we ignore the bulk of the rest of the network traffic out there. That's where we get in trouble repeatedly.
On the bright side, I do see the idea of taking an analytical approach to information security slowly spreading throughout the community. I think it's only a matter of time before one organization after another wakes up to the fact that their 1990s era signature-based approaches are only one part of the larger solution. With proper analysis and monitoring of network data and network traffic comes knowledge. And with knowledge comes the realization that what you don't know is often a lot scarier than what you do know.