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Understanding the advanced persistent threat

Think you know all you need to know about the advanced persistent threat? We'll define APT and dispel a few myths.

The term advanced persistent threat, or APT, joined the common vocabulary of the information security profession...

in mid-January, when Google announced its intellectual property had been the victim of a targeted attack originating from China. Google wasn't alone; more than 30 other technology firms, defense contractors and large enterprises had been penetrated by hackers using an array of social engineering, targeted malware and monitoring technologies to quietly access reams of sensitive corporate data.

Google's public admission put a high-profile face on targeted attacks and the lengths attackers would go to gain access to proprietary corporate and military information. It also kicked off a spate of vendor marketing that promised counter-APT products and services that have only served to cloud the issue for security managers and operations people.

In this article, we'll define APT, dispel some myths and explain what you can do about this adversary.


The United States Air Force coined the phrase advanced persistent threat in 2006 because teams working within the service needed a way to communicate with counterparts in the unclassified public world. Department of Defense and intelligence community members typically assign classified names to specific threat actors, and use the term intrusion set to describe activities by those threat actors. If the USAF wanted to talk about a certain intrusion set with uncleared personnel, they could not use the classified threat actor name. Therefore, the USAF developed the term APT as an unclassified moniker.

It is crucial to this discussion to recognize that APT is a proper noun. APT refers to specific threat actors; APT does not refer to vaguely unknown and shadowy Internet forces. The term is most frequently applied to distinct groups operating from the Asia-Pacific region. Those knowledgeable about APT activities can conduct an honest debate as to whether the term should be used to refer ONLY to certain Asia-Pacific actors, or if it can be expanded as a general classifier. In other words, if adversaries in Eastern Europe operate using the same tools, tactics, and procedures as traditional APT, should these actors also bear the APT label?

The answer to this question depends on the person asking it. An information security practitioner in a private organization will typically not care if the threat actors attacking an enterprise originate in the Asia-Pacific or Eastern European regions. The reason is that the practitioner will likely take the same defensive actions regardless of the location or nationality of the adversary.

However, someone with the legal and/or national security authority to apply diplomatic, intelligence, military, or economic (DIME) pressure would certainly want to identify the origin of an attack. For the purposes of this article, aimed at information security practitioners, it is not necessary to answer the "who" question definitively. However, those who do have elements of DIME power should take attribution statements by Google and other victims seriously.

Most of those actively countering APT activity describe the adversary in the following manner:

Advanced means the adversary can operate in the full spectrum of computer intrusion. They can use the most pedestrian publicly available exploit against a well-known vulnerability, or they can elevate their game to research new vulnerabilities and develop custom exploits, depending on the target's posture.

Persistent means the adversary is formally tasked to accomplish a mission. They are not opportunistic intruders. Like an intelligence unit they receive directives and work to satisfy their masters. Persistent does not necessarily mean they need to constantly execute malicious code on victim computers. Rather, they maintain the level of interaction needed to execute their objectives.

Threat means the adversary is not a piece of mindless code. The opposition is a threat because it is organized and funded and motivated. Some people speak of multiple "groups" consisting of dedicated "crews" with various missions.

In brief, APT is an adversary who conducts offensive digital operations (called computer network operations or perhaps computer network exploitation) to support various state-related objectives. APT is characterized by devotion to maintaining some degree of control of a target's computer infrastructure, acting persistently to preserve or regain control and access. Unclassified briefings by counter-intelligence and military analysts use the term "aggressive" to emphasize the degree to which APT pursues these objectives against a variety of government, military, and private targets.

APT Impact
Analysts currently assess APT activities as supporting four main goals.


  • Political objectives such as maintaining internal stability.
  • Economic objectives that rely on stealing intellectual property from victims. Such IP can be cloned and sold, studied and underbid in competitive dealings, or fused with local research to produce new products and services more cheaply than the victims.
  • Technical objectives that further their ability to accomplish their mission. These include gaining access to source code for further exploit development, or learning how defenses work in order to better evade or disrupt them. Most worringly is the thought that intruders could make changes to improve their position and weaken the victim.
  • Military objectives that include identifying weaknesses that allow inferior military forces to defeat superior military forces.



Beginning in January and peaking in February and March, many elements of the digital security community focused their attention on APT. Unfortunately, some of those speaking about the problem quickly found themselves echoing statements and questionable research offered by parties who were not familiar with APT. Several factors contributed to an overall sense of confusion, with some of the more trustworthy voices competing with parties who would have been better advised to stay in the background.

Several factors caused this phenomenon:

  • Besides Google's public statement, and subsequent secondhand reporting about allegedly affected peer companies, very little original data was available. Without details to discuss, the security community turned to almost anyone willing to talk about the incident. In too many cases, the speakers turned out to be vendors who saw APT as a marketing angle to rejuvenate slumping security spending. RSA Conference 2010 featured many companies selling counter-APT products, hoping to capitalize on the new hot topic of 2010..
  • McAfee reported it was analyzing malware that it claimed to be associated with the Google incident, independently assigning the name "Aurora" to the affair thanks to a path found in the malware. In late March, McAfee blamed "the fog of war" for mistakenly confusing a Vietnamese-targeted botnet with Google incident malware. Unfortunately, by associating this false lead with the Google incident, McAfee prompted a variety of security researchers to direct their efforts on code that likely had nothing to do with the Google incident.
  • Many analysts too narrowly focused on the elements of the incident that they could best understand, regardless of the real nature of the event. For example, companies specializing in botnet research assumed botnets were involved, and talked about the Google incident in those terms. Others who focus on identifying vulnerabilities and developing exploits, concentrated on a flaw in Internet Explorer (patched by MS10-002) presumably leveraged by intruders to gain access to Google resources. Unfortunately, botnets have nothing to do with APT, and vulnerabilities, exploits, and malware are only elements of APT incidents -- not the core feature of them.


When the Google attack entered the public arena, many people wondered if APT was something new. The answer to this question depends on one's perspective, plus understanding some history. As mentioned earlier, the term APT is approximately 4 years old. It entered the common lexicon in early 2010 with the publicity garnered by Google's bold proclamation. However, consulting companies, particularly Mandiant have been conducting public webcasts and presentations discussing APT by name since 2008.

Prior to the 2006 invention of the APT term, news stories of Chinese intruders attacking military and government organizations bore the label "Titan Rain." For example, a 2005 Time magazine article by Nathan Thornburgh titled "The Invasion of the Chinese Cyberspies" described battles fought by Shawn Carpenter, then defending Sandia National Laboratories. That story mentioned Carpenter's experience with similar intruders dating back to late 2003. Even in 1998, while serving as a captain in the Air Force Computer Emergency Response Team, we encountered adversaries that many would now label APT.

Some would even argue that nothing about APT is new. To the extent that espionage is as old as warfare itself, some claim APT activity is just spying another form--and not even a new medium, given the history of computer espionage dating from Cliff Stoll's work in the 1980s.

I argue that APT is new if those asking the question move beyond two-dimensional thinking. Considering APT activity in terms of offender, defender, means, motive, and opportunity, APT is clearly new. Points for the "old" camp include the identity of the offender (nation-states) and the motive (espionage). Points for the "new" camp make a stronger argument:

Defender: I break APT targets into four phases: 1) late 1990s - military victims; 2) 2000-2004 - non-military government victims; 3) 2005-2009 - defense industrial base; 4) 2009-present - intellectual property-rich targets and software companies. (Unfortunately there are clear examples of earlier victims, but these dates roughly cover most known cases.) The assault conducted during phases 3 and 4 is unprecedented, meaning entirely new classes of defenders must protect themselves from attackers previously a concern for the military.

Means: Too many critics focus on malware, ignoring (or being unaware) of the impressive management and administration applied to repeatedly attempting to access, or preserving access, to target organizations. APT incidents are not hit-and-run, smash-and-grab affairs.

Opportunity: The explosion of Internet connectivity in the last decade and the extreme distribution of sensitive data to end points provides cheap, low-risk, remote access options for intruders, unlike anything available to human spies.

On balance, I argue APT is new, at least when considered from the perspective of non-military targets, and remembering that phase 3 APT activity began in 2003 and became a significant problem in 2005.


The majority of this article has focused on describing APT and its history, because battling this adversary does not require a technical solution. The most effective counter-APT weapon is a trained and knowledgeable information security analyst. Many security vendors have adopted APT in their marketing literature. Some offer to find APT on a potential victim's network. Others have even registered APT-themed domain names.

Tools are always helpful, but the best advice I can provide is to educate business leaders about the threat so that they support organizational security programs conducted by competent and informed staff.

A second question one is likely to ask follows: How do I know if I am an APT target? Contact your local Federal Bureau of Investigation office. One of the biggest game-changers in counter-APT awareness developed during the last several years is taking the form of visits by FBI and military or counter-intelligence specialists to potential victims. It's difficult to deny a security breach when representatives from a national security agency reveal excerpts from proprietary data or intellectual property and ask "does this data belong to you?" If you have not already engaged your organization's leaders in a counter-APT conversation, requesting a threat briefing from the local FBI office is an excellent way to promote managerial attention.

On a technical level, building visibility in to one's organization will provide the situational awareness to have a chance to discover and hopefully frustrate APT activities. Without information from the network, hosts, logs, and other sources, even the most skilled analyst is helpless. Thankfully, obtaining such information is not a new challenge, and most security shops should be pursuing such programs already. The goal of counter-APT operations should be to make it as difficult as possible for the adversary to steal intellectual property; "increasing the cost per megabyte," to quote the NSA's Tony Sager, is the goal.

Richard Bejtlich is director of incident response for General Electric, and serves as principal technologist for GE's Global Infrastructure Services division.Send comments on this article to [email protected].

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