The Origin of the Term Indicators of Compromise (IOCs)

I am an historian. I practice digital security, but I earned a bachelor's of science degree in history from the United States Air Force Academy. (1)

Historians create products by analyzing artifacts, among which the most significant is the written word.

In my last post, I talked about IOCs, or indicators of compromise. Do you know the origin of the term? I thought I did, but I wanted to rely on my historian's methodology to invalidate or confirm my understanding.

I became aware of the term "indicator" as an element of indications and warning (I&W), when I attended Air Force Intelligence Officer's school in 1996-1997. I will return to this shortly, but I did not encounter the term "indicator" in a digital security context until I encountered the work of Kevin Mandia.

In August 2001, shortly after its publication, I read Incident Response: Investigating Computer Crime, by Kevin Mandia, Chris Prosise, and Matt Pepe (Osborne/McGraw-Hill). I was so impressed by this work that I managed to secure a job with their company, Foundstone, by April 2002. I joined the Foundstone incident response team, which was led by Kevin and consisted of Matt Pepe, Keith Jones, Julie Darmstadt, and me.

I Tweeted earlier today that Kevin invented the term "indicator" (in the IR context) in that 2001 edition, but a quick review of the hard copy in my library does not show its usage, at least not prominently. I believe we were using the term in the office but that it had not appeared in the 2001 book. Documentation would seem to confirm that, as Kevin was working on the second edition of the IR book (to which I contributed), and that version, published in 2003, features the term "indicator" in multiple locations.

In fact, the earliest use of the term "indicators of compromise," appearing in print in a digital security context, appears on page 280 in Incident Response & Computer Forensics, 2nd Edition.

From other uses of the term "indicators" in that IR book, you can observe that IOC wasn't a formal, independent concept at this point, in 2003. In the same excerpt above you see "indicators of attack" mentioned.

The first citation of the term "indicators" in the 2003 book shows it is meant as an investigative lead or tip:

Did I just give up my search at this point? Of course not.

If you do time-limited Google searches for "indicators of compromise," after weeding out patent filings that reference later work (from FireEye, in 2013), you might find this document, which concludes with this statement:

Indicators of compromise are from Lynn Fischer, Lynn, "Looking for the Unexpected," Security Awareness Bulletin, 3-96, 1996. Richmond, VA: DoD Security Institute.

Here the context is the compromise of a person with a security clearance.

In the same spirit, the earliest reference to "indicator" in a security-specific, detection-oriented context appears in the patent Method and system for reducing the rate of infection of a communications network by a software worm (6 Dec 2002). Stuart Staniford is the lead author; he was later chief scientist at FireEye, although he left before FireEye acquired Mandiant (and me).

While Kevin, et al were publishing the second edition of their IR book in 2003, I was writing my first book, The Tao of Network Security Monitoring. I began chapter two with a discussion of indicators, inspired by my Air Force intelligence officer training in I&W and Kevin's use of the term at Foundstone.

You can find chapter two in its entirety online. In the chapter I also used the term "indicators of compromise," in the spirit Kevin used it; but again, it was not yet a formal, independent term.

My book was published in 2004, followed by two more in rapid succession.

The term "indicators" didn't really make a splash until 2009, when Mike Cloppert published a series on threat intelligence and the cyber kill chain. The most impactful in my opinion was Security Intelligence: Attacking the Cyber Kill Chain. Mike wrote:

I remember very much enjoying these posts, but the Cyber Kill Chain was the aspect that had the biggest impact on the security community. Mike does not say "IOC" in the post. Where he does say "compromise," he's using it to describe a victimized computer.

The stage is now set for seeing indicators of compromise in a modern context. Drum roll, please!

The first documented appearance of the term indicators of compromise, or IOCs, in the modern context, appears in basically two places simultaneously, with ultimate credit going to the same organziation: Mandiant.

The first Mandiant M-Trends report, published on 25 Jan 2010, provides the following description of IOCs on page 9:

The next day, 26 Jan 2010, Matt Frazier published Combat the APT by Sharing Indicators of Compromise to the Mandiant blog. Matt wrote to introduce an XML-based instantiation of IOCs, which could be read and created using free Mandiant tools.

Note how complicated Matt's IOC example is. It's not a file hash (alone), or a file name (alone), or an IP address, etc. It's a Boolean expression of many elements. You can read in the text that this original IOC definition rejects what some commonly consider "IOCs" to be. Matt wrote:

Historically, compromise data has been exchanged in CSV or PDFs laden with tables of "known bad" malware information - name, size, MD5 hash values and paragraphs of imprecise descriptions... (emphasis added)

On a related note, I looked for early citations of work on defining IOCs, and found a paper by Simson Garfinkel, well-respected forensic analyst. He gave credit to Matt Frazier and Mandiant, writing in 2011:

Frazier (2010) of MANDIANT developed Indicators of Compromise (IOCs), an XML-based language designed to express signatures of malware such as files with a particular MD5 hash value, file length, or the existence of particular registry entries. There is a free editor for manipulating the XML. MANDIANT has a tool that can use these IOCs to scan for malware and the so-called “Advanced Persistent Threat.”

Starting in 2010, the debate was initially about the format for IOCs, and how to produce and consume them. We can see in this written evidence from 2010, however, a definition of indicators of compromise and IOCs that contains all the elements that would be recognized in current usage.

tl;dr Mandiant invented the term indicators of compromise, or IOCs, in 2010, building off the term "indicator," introduced widely in a detection context by Kevin Mandia, no later than his 2003 incident response book.

(1) Yes, a BS, not a BA -- thank you USAFA for 14 mandatory STEM classes.

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