Abstract: Armed military-grade drones have been a central tool for the United States to counter the threat posed by al-Qa`ida and the Islamic State. It is therefore not surprising that the West’s use of drones has been a subject of intense interest for these groups and their supporters online. Indeed, the jihadi community for years has sought ways to disrupt and limit the effectiveness of armed drones and to deploy its own drones in offensive ways. As the United States and other countries begin to deploy counter drone solutions to mitigate the jihadis’ offensive drone threat, it would be wise to game out creative and inexpensive ways to defeat countermeasures being deployed by the West so the jihadis’ response to those methods can be anticipated and pre-empted.
In early October 2016, the Islamic State used an explosive-laden drone to kill two Kurdish fighters and injure two French Special Forces soldiers. The group was able to achieve the feat not by some sophisticated technical breakthrough, but rather through a combination of deception (hiding the explosives inside the device) and creativity (detonating the device after it had been downed by Kurdish forces and was taken back to their base for inspection).1 This event, and other similar incidents involving terrorist use of explosive-carrying drones over the past year, has led to a push by the United States and other nations to more rapidly field a plethora of drone countermeasures.a These solutions range from drone-disabling guns and small, armed attack drones to eagles and electronic and cyber countermeasures.b
As these various approaches are pursued, it is worth considering how groups like the Islamic State are going to respond to the deployment of these systems and how they are going to try and defeat them.2
The way the jihadi community has sought previously to counter the West’s use of armed drones provides a useful window in this regard, as the topic has been a thread of online discussion among jihadi organizations and their supporters for years. This article provides a general overview of those discussions on Arabic language jihadi forums, drawing on postings between July 2005 and December 2013 collected by the Combating Terrorism Center, as well as other open source material.3 This article specifically outlines the creative and resourceful ways that jihadis have sought to counter armed military drones since 9/11,c and it does so with the aim of providing insight into how the jihadi community might defeat U.S. countermeasures against jihadi drones.
The Jihadis’ Approach
The mujahidin in Somalia should be careful of the air bombardments and should benefit from the art of gathering and dispersion experience, as well as movement, night and day transportation, camouflage, and other techniques related to war tricks.
—Letter from al-Qa`ida operative Atiyyah Abd al-Rahman to Mujahidin in Somalia (al-Shabaab)4
The facts prove that the American technology and advanced systems cannot capture a mujahid if he does not make a security violation that will lead them to him. Commitment to operational security makes his technological advancement a waste.
—Letter from Usama bin Ladin to Atiyyah5
The two quotes from Atiyyah and bin Ladin above speak to the important role countermeasures, counterintelligence, and defensive strategies have played and continue to play in the survival and endurance of groups like al-Qa`ida and the Islamic State. They reinforce two points. First, the threat to these groups and their allies across the globe from armed drone strikes is real. And second, good operational security is not only critical to their survival but is also required to counter or nullify the advantages that superior U.S. technology affords. To protect themselves and limit the effects of drones, writers active on jihadi forums have released tips and operational tradecraft guides, which provide recommendations one should follow to avoid being targeted by a drone, for their followers. To draw upon the collective strength and knowledge of their community, jihadi forum administrators have also opened the discussion to the masses, as an attempt to crowdsource countermeasures and other solutions—and they have been doing so since at least 2011.6 Cash prizes have even been offered.7
The approach that the jihadi community has taken to this issue is fairly thorough, as in the discussion threads online one can easily see jihadi forum members conduct vulnerability assessments of drones. There were examples of different individuals—or small groups—trying to find weaknesses in each component, from sensors and encryption to spies, that could be exploited to defeat a drone, limit its accuracy, or enhance survivability.
Such investment in countermeasures, is certainly not new as terrorist groups of all persuasions have long sought ways to reduce the effectiveness of their adversaries’ actions and to learn from others.8 As noted by Brian Jackson and his colleagues at RAND,9 countermeasures, even when successful, usually only have a limited shelf life, necessitating consistent focus for any terror group.10
To make sense of terror counter-technology dynamics, Brian Jackson and his colleagues at RAND developed a typology with four meta-categories. This typology is useful in that it helps to situate analytically the countermeasures deployed by terrorist groups. The four meta-categories created by RAND include: altering operational practices, making technological changes or substitutions, avoiding the technology, and attacking the technology.11 While a terrorist group’s effort to counter drones can usually be placed into one of these categories, they are not mutually exclusive. As revealed below, sometimes a terror group’s approach is more complex and fits into several of them.d
Screen capture from a video released by Jund al-Aqsa in September 2016 showing a munition being dropped from a commercial drone in Syria
The solutions proposed by the jihadi community in its online marketplace for ideas are best thought of as a spectrum that ranges from the silly to the somewhat sophisticated. A jihadi who went by the name Abu `Ubayda `Abdullah al-`Adam served as a pioneer in this space and added some institutional structure and formality to the jihadis’ discussions on the topic. Before his reported death in a drone strike in Pakistan during the spring of 2013, U.S. intelligence agencies believed al-`Adam served as al-Qa`ida’s intelligence chief.12 He also authored and released a series of “reports”—all identified by the Terrorism Industry title that they carried—that provided decentralized advice on operational tradecraft and security to anyone perusing the jihadi forums. Several of al-`Adam’s reports focused on drone strikes so that the specific practices that contributed to the strikes could be diagnosed and corrected. What follows is a summary, organized along the lines of the RAND typology described above, of the countermeasures that al-`Adam and other jihadi sympathizers have discussed, recommended, or practiced.
Altering Operational Practices/Avoiding the Technology
Physical Responses and Efforts to Conceal
One major area of discussion by jihadi forum members online were efforts to harden and camouflage facilities. As explained by al-`Adam, “the camouflage is used to mislead [the enemy], and prevent [one from] becoming a clear target. For example: The place that we use to build VIEDs [Vehicle-Borne Improvised Explosive Devices] should be covered. It is a big mistake to use an open space to build VIEDs even if we are doing that here, in Afghanistan, or in a secure area [that] cannot be reached by the enemy.”13 He made the consequences of not concealing your position clear: “If you do your work in an open area, you’ll become an easy and open target for the unmanned aerial vehicles and the spying planes.”14 In addition to working inside and covering sensitive locations, other jihadis responded to this thread online with more trivial ideas, such as hiding under dense trees, burning tires (so that a smokescreen would be created), and digging tunnels.15
The most sophisticated concealment measure investigated by jihadi forum users online was a line of counter-surveillance clothing created by New York City designer Adam Harvey in 2013.16 The product that Harvey developed, in which the jihadis took particular interest in and reposted, were garments made out of material that masks and suppresses body heat—material that, as a video released on Harvey’s website illustrates, limits the effectiveness of forward-looking infrared imaging (FLIR) systems, a key sensor drones use for targeting.17 In addition to having an awareness of Harvey’s work, jihadi members online also discussed how to create homemade remedies, with one user suggesting that sand should be sewn between two pieces of clothing to achieve a similar effect.18
Hardening facilities was an additional area of focus with another prominent writer, Abu `Abd al-Rahman al-Qahtani, suggesting people should move their offices to the basement of a house, work out of caves, or place sand bags on their roofs to limit attrition and dampen the blast effects of strikes.19
Altering Personal Tactics, Techniques, and Procedures (TTPs) to Reduce Targeting and Evade Drones
Discussions regarding changes to personal TTPs were predicated on a general understanding of the sensors with which most military grade drones are equipped. This included jihadi contributors having an awareness of high-resolution cameras and thermal imaging technology that drones can have on board and the ability of these platforms to work as “efficiently at night as they do in the day time.”20 There was also an awareness that drones study their targets’ movement and pattern of life. As al-`Adam explained in Episode 12 of his Terrorism Industry series, “the unmanned aerial vehicle (UAV), especially, is able to determine your location and watch your movements and there does not need to be a mobile phone [in your possession]. The UAV has the ability to precisely pinpoint your position via your movements.”21 To address these issues, al-Qahtani suggested common operational security practices such as frequently changing travel routines and bed-down locations (to include shifting to those far away from areas with known drone activity).22 Abdullah al-`Adam, citing the reasons and mistakes that led to the assassination of Abu Hamza al-Rabia—an Egyptian who served as al-Qa`ida’s international operations planner before his death by drone strike in 2005—recommended that changes also be made to the circle around oneself after a failed assassination attempt.23 Al-`Adam believed that al-Rabia’s demise was a result of him not making these changes after a prior attempt on his life.24
Not surprisingly, the use of electronic devices to evade drone surveillance and associated strikes was a rich thread of discussion.e It was on this topic, perhaps more than any other, that the jihadi community’s concerns over operational security were most evident.25 It was also the area where the countermeasures and operational tradecraft guidance was the most specific.
Attacking the Technology
As one might expect, a considerable amount of attention was paid to devising ways to attack, disrupt, or sabotage drones and the logistics chain associated with them.
One particular area of interest for the jihadis was disrupting the signals that guide and control drones, a practice commonly known as ‘jamming.’ For this to be accomplished, the actor seeking to disrupt a system needs to deploy radio or other electronic measures to interfere with a specific drone’s system, which—if executed properly—would limit that device’s ability to operate effectively. The jamming solutions proposed by jihadi sympathizers online were mostly do-it-yourself in character and consisted of, for example, using “a regular water pump generator… after attaching to it a 30-meter copper pipe,” “old pieces of [unspecified] communications equipment, because their frequencies are very strong,” or the “Russian-made Rascal device.”26 The latter is software that broadcasts “frequencies or a band of frequencies to cut off the communications or to jam the frequencies that are used to control the drone.”27 More recently, in a forum post from November 2015, a participant encouraged Islamic State fighters to use a GPS signal and radio frequency jammer called Wave Bubble.28
Intercepting Feeds, GPS Spoofing, and Hacking
Another related area of vulnerability that jihadi forum users focused on were the data links/feeds that allow drones to communicate and share data with their controllers. Particular emphasis in these discussions was placed on intercepting drone feeds. In late 2009, media reports surfaced detailing the ability of Kataib Hezbollah, a Shi`a militant group active in Iraq, to intercept data from U.S. drones.29 According to these accounts, the Shi`a militants intercepted the “feeds by taking advantage of an unprotected communications link in some of the remotely flown planes’ systems.”30 They did so by using a Russian software program called SkyGrabber that was “intended to steal satellite television” and was available for purchase for $26 on the internet.31 By creatively repurposing this software, Kataib Hezbollah was able to “download real-time video feeds from American surveillance drones as they flew over Iraq … [which allowed them to] both monitor and evade U.S. operations.”32 The U.S. military learned of the problem after “they apprehended a Shiite militant whose laptop contained files of intercepted drone video feeds.”33 Jihadi forum contributors were aware of this software, as their posts directly referenced both the software and press coverage about its use by insurgents in Iraq.34
Jihadi forum users also had awareness of successful ‘spoofing’ of a small, commercially purchased drone by a team at the University of Texas at Austin’s Radionavigation Laboratory, which was featured in U.S. media in June 2012. The researchers were able to take control of the drone’s GPS navigation system so they could fly and direct the device themselves.35 It should be noted that military-grade drones, like the Reaper and Predator, are more sophisticated, and their feeds have higher levels of encryption than commercially available drone variants, making it more difficult for an external party to spoof or otherwise send those more advanced versions false instructions. Yet, a number of incidents reveal that the encryption of military-grade drone feeds is a cat-and-mouse game being played out between the United States and its adversaries, as America’s enemies are looking for—and in some cases have previously found—ways to gain access to military drone data feeds.
A number of cases that have been publicized involve Iran and its proxies, which is not necessarily surprising as Hezbollah successfully tapped into Israeli drone feeds in 1996, an advantage that led to the 1997 massacre of 11 Israeli commandos during a cross-border operation in Lebanon.36 (Hezbollah’s ability to gain access to Israel’s drone feeds at the time allowed it to gain insights into the facilities the Israelis were monitoring. This meant that instead of the Israeli targeting operation surprising Hezbollah fighters, they were there waiting for it.) In 2011, Iran claimed that it was able to take over the GPS system of the United States’ advanced, stealth RQ-Sentinel drone while it was conducting a reconnaissance mission near Iranian territory.37 The United States has disputed the charge and claims that Iran recovered the drone after it crash-landed within its borders.38
Another form of drone takeover can be achieved via hacking. For example, in 2013, an enterprising programmer based in the United States developed software called SkyJack that allows the user to seek “the wireless signal of any other [commercial] drone in the area.”39 The program then “forcefully disconnects the wireless connection of the true owner of the target drone, then authenticates with the target drone pretending to be its owner,” which allows the user to take control of the drone.40 All that was required to facilitate this takeover was “a Parrot AR.Drone 2, a Raspberry Pi, a USB battery, an Alfa AWUS036H wireless transmitter, aircrack-ng, node-ar-drone, node.js, and … SkyJack software.”41 Another researcher has developed a way to hack into DSMx, “a widely used remote control protocol for operating hobbyist drones, planes, helicopters, cars, and boats,” allowing the hijacker to control other nearby drones.42 Given the jihadis’ interest in counter-drone technologies, it has to be assumed that both these tools have caught their attention.
Homing Beacons, Spies, and Counterintelligence
Discussions on the jihadi forums also centered on attempts to attack and defeat the methods that the jihadis believe link a drone missile to its target. The majority of their attention focused on learning about homing beacons that transmit electromagnetic or infrared signals and local spies who they believe place the beacons or use other means to identify which facility or individual should be targeted.43 Official jihadi publications have even included pictures of specific beacons that were allegedly recovered from spies in Pakistan’s tribal areas.44 To defeat these beacons, al-Qahtani send out a request across the forums for additional information on these devices and how they work. He specifically wanted to know “the frequency these waves work on” and recommended that people send in strategies for how they could be defeated.45
Jihadi terror groups have also set up, or bolstered, counterintelligence units to root out spies.f These efforts have been accompanied by efforts to share knowledge regarding how spies operate as well as practical steps that group members can take to help identify them or limit their effectiveness. The information being shared ranges from the obvious—“anyone who uses communication devises should be secretly tracked”—to the more specific, including information aimed at creating awareness about methods used by local and state intelligence units to recruit spies.46 For example, a significant portion of issue 19 of the Terrorism Industry series provides a detailed overview of the method used by the Pakistani Army to coerce a local shopkeeper in Waziristan to target a wanted individual. According to the report, the Pakistani Army got the shopkeeper to act on its behalf through an incremental approach that started with an exchange of small favors involving money.47 This created an environment where the shopkeeper became—even if on a small scale—indebted to his recruiter and took actions that he might not have otherwise, such as placing a tracking device in a militant’s car.48 The sharing of these types of anecdotal stories with online jihadi sympathizers is designed to both educate those on the forums and to serve as a cautionary tale to deter future spies and potential collaborators, as the story told in issue 19 ends with the local spy being discovered and killed.49
Although many of the countermeasures outlined above are amateurish and driven by common sense, they also speak to a certain level of focus and commitment by the jihadi community to achieve two goals: 1) to understand their adversaries (and their strengths) and 2) to be resourceful and work with what they have. A central lesson for the United States and its allies, given the cost and time associated with the development of drone countermeasures, is that efforts should be made—and made early—to defeat the countermeasures being deployed by the West so the jihadis’ response to those methods can be anticipated and pre-empted.
Two ways to achieve this, if not already being done, would be for the United States to integrate such efforts into its annual Black Dart drone exercise and to sponsor a competition—accessible by a wide range of participants—that rewards the discovery of low-cost and practical ways to overcome Western drone defeat devices. Such an approach would take a page out of the jihadi playbook and could produce interesting revelations about the tools the United States plans to deploy in the field, and it could also highlight other drone defense gaps that have yet to be considered. To protect any vulnerabilities, it would be important not to publicize the findings from these efforts, as the jihadi community is paying attention to media coverage of these types of topics.
Another major takeaway is that detailed drone countermeasure conversations by jihadis online should be mined for useful solutions that can be exploited by U.S. forces and their partners in the field. The jihadis identification of software like SkyGrabber and other similar programs that are more current could prove useful to understanding the myriad mix of countermeasures that may be deployed to circumvent or fool drone defeat systems. CTC
Don Rassler is Director of Strategic Initiatives at the Combating Terrorism Center at the U.S. Military Academy at West Point. His research is focused on terrorist innovation and the changing dynamics of Afghanistan’s and Pakistan’s militant landscapes. Follow @donrassler
[a] Many of these drone countermeasure systems have been in production for years. For background, see Colin Clark, “New Weapons Spell Death for Drones: the Countermeasure Dance,” BreakingDefense.com, October 13, 2014.
[b] Since the early 2000s, the U.S. Department of Defense’s Black Dart exercise has served as a venue to test out these various types countermeasures. For background, see “Black Dart: The U.S. Military’s Countermeasure against Drones,” NBC Nightly News, August 8, 2016. For background on the use of eagles to take down commercial drones, see Kelsey D. Atherton, “Trained Police Eagles Attack Drones on Command,” Popular Science, February 1, 2016.
[c] Due to their popularity when data was collected (2014), attention was specifically placed on three forums: Shumukh al-Islam, Al-Fida, and Ansar al-Mujahidin. The CTC gathered and cataloged all of the material it could find on these three forums that directly referenced or commented on drones, unmanned aerial vehicles, remote control planes, or other similar search terms during a search it conducted during the early months of 2014. This search process yielded 218 drone-related posts that were included on the forums between July 2005 and December 2013. The material that was recovered as part of this process fell into three categories: 1) official publications or statements made by jihadi groups; 2) discussions threads or posts submitted by senior forum writers or forum administrators (i.e. individuals who manage and run the forum sites and serve as links between jihadi organizations and other users of the forums); and 3) posts and comments made by forum members, individuals who are believed to be jihadi sympathizers. There are a number of problems and limitations associated with this approach, and in using the second and third categories of forum-derived information specifically. First, while the forums have served as an aggregator of jihadi content, it is not clear how representative the material posted on the forums is of the broader Sunni jihadi collective. Second, since a direct connection usually cannot be made between jihadi terrorist groups and the statements made by forum members and administrators, the latter category of information functions only as a proxy for the views of jihadi terrorist entities themselves. This is not to say that the views of administrators and forum members are not useful, but rather that researchers should be cautious about making strong conclusions about jihadi groups from this material alone. Third, due to concerns over surveillance and forums being targeted by government agents as a form of collection, forums users typically mask their true identities. Thus, it is not possible to establish which forum users are genuine jihadi sympathizers and to differentiate them from those who are not. Readers should read this article with these caveats in mind. For background on Arabic language jihadi forums, see Edna Eraz, Gabriel Weimann, and Aaron Weisburd, “Jihad, Crime and the Internet: Content Analysis of Jihadist Forum Discussions,” Report Submitted to the National Institute of Justice, October 31, 2011, and Mohammed al-Musawi, “Cheering for Osama: How Jihadists Use Internet Discussion Forums,” Quillam Foundation, August 2010.
[d] As noted by RAND in its report, “reflecting this complexity, the four strategies are likely better viewed as the extremes of four overlapping sets … in which specific counterefforts may draw on one or more of the basic strategies in an effort to defeat or circumvent a specific defensive technology.” Brian A. Jackson et al., Breaching the Fortress Wall: Understanding Terrorist Efforts to Overcome Defensive Technologies (Santa Monica, CA: RAND Corporation, 2007), p. 118.
[e] Another interesting thread of discussion contained conversations about the tactical and operational behavior of drones in the area and the apparent trends or signs that the jihadis have noticed about their altitude and other performance immediately before a strike. For background, see `Abir Sabil5, “A Temporary Solution to the UAV: Participate with what you Know,” Ansar al-Mujahidin forum, October 2012.
[f] Hamas has set up similar units to hunt down Israeli collaborators. See Jackson et al., Breaching the Fortress Wall, p. 25; for a comprehensive overview of terrorism and counterintelligence, see Blake W. Mobley, Terrorism and Counterintelligence: How Terrorists Avoid Detection (New York: Columbia University Press, 2012).
 Michael S. Schmidt and Eric Schmitt, “Pentagon Confronts a New Threat from ISIS: Exploding Drones,” New York Times, October 11, 2016.
 For background on the countermeasures pursued by terrorists and organizational learning by terror organizations, see Brian A. Jackson et al., Breaching the Fortress Wall: Understanding Terrorist Efforts to Overcome Defensive Technologies (Santa Monica, CA: RAND Corporation, 2007); Brian A. Jackson et al., Aptitude for Destruction: Volume 1 – Organizational Learning in Terrorist Groups and its Implications for Combating Terrorism (Santa Monica, CA: RAND Corporation, 2005); Brian A. Jackson et al., Aptitude for Destruction: Volume 2 – Case Studies of Organizational Learning in Five Terrorist Groups (Santa Monica, CA: RAND Corporation, 2005).
 The author would like to thank Muhammad al-`Ubaydi, a research associate at the Combating Terrorism Center, for his assistance in finding and collating all of this material.
 “Letter to the Mujahidin in Somalia dtd 28 December 2006,” Bin Laden’s Bookshelf, Office of the Director of National Intelligence.
 “Letter to Shaykh Mahmud,” Bin Laden’s Bookshelf, Office of the Director of National Intelligence.
 Muhib al-Jihad al-Akbar, “The Drones: A Very Important Announcement,” Shumukh al-Islam Network, March 22, 2013. For an example of a similar (and earlier) post from the Ansar al-Mujahidin forum, see Mujahid al-Bahar, “Important: A Workshop to Collection Information on the Drones,” Ansar al-Mujahidin forum, November 2011. Specific groups in the Afghanistan-Pakistan region have also made similar requests in their publications. See the first issue of Azan, released in March 2013. See also Abu `Abd-al-Rahman al-Qahtani, “The Dirty UAV and the Best Ways to Deal with it,” Shumukh al-Islam Network, May 2013.
 For background on this issue, see Jackson et al., Breaching the Fortress Wall.
 Ibid, p. 7.
 For background, see Bill Roggio, “Al Qaeda Intelligence Chief Reported Killed in a Drone Strike,” Long War Journal, April 22, 2013. Al-`Adam also wrote under the name Abu Ubaydah al-Maqdisi.
 Abu `Ubayda `Abdullah Al-`Adam, Terrorism Industry: Episode 8, September 2010.
 `Abir Sabil5, “A Temporary Solution to the UAV: Participate with what you Know,” Ansar al-Mujahidin forum, October 2012. These online discussions covered the same ground as a jihadi document discussing drone countermeasures discovered in Mali. See “The Al-Qaida Papers: Drones,” Associated Press, February 2013. The smokescreen idea sparked off a debate online with some posters recognizing that RPA sensors likely have the ability to see through smoke; see also Abduallah Saqar, “The Unmanned Aerial Vehicles,” Fateh al-Islam Organization, August 2013.
 For background, see Tim Maly, “Anti-Drone Camouflage: What to Wear in Total Surveillance,” Wired, January 17, 2013; and https://ahprojects.com/projects/stealth-wear/.
 Muhib al-Jihad al-Akbar, “The Drones: A Very Important Announcement!”
 Al-Qahtani. See also “The Al-Qaida Papers: Drones.”
 For quote, see al-Qahtani. For other background, see Saqar.
 Abu `Ubayda `Abdullah al-`Adam, Terrorism Industry: Episode 12, September 2010.
 Al-Qahtani. See also “The Al-Qaida Papers: Drones.”
 Al-`Adam, Terrorism Industry: Episode 12.
 Ibid. For background on al-Rabia, see “Al-Qaeda Number Three ‘Killed by CIA Spy Plane’ in Pakistan,” Telegraph, December 4, 2005, and “Al-Qaeda No. 3 Dead: But How?” CNN, December 4, 2005.
 For background, see al-`Adam, Terrorism Industry: Episode 12 and al-Qahtani.
 “The Al-Qaida Papers: Drones.”
 “Jihadist Suggests IS Use GPS Jammers to Take Down Drones, Confuse Coalition Pilots,” SITE Intelligence Group, November 5, 2015.
 Siobhan Gorman, Yochi J. Dreazen, and August Cole, “Insurgents Hack U.S. Drones,” Wall Street Journal, December 17, 2009.
 Marc Goodman, “Criminals and Terrorists Can Fly Drones Too,” Time, January 31, 2013.
 Gorman, Dreazen, and Cole.
 Al-Qahtani; “The Al-Qaida Papers: Drones.”
 Al-Qahtani. For background on Todd Humphrey’s work, see John Roberts, “Exclusive: Drones Vulnerable to Terrorist Hijacking, Researchers Say,” Fox News, June 25, 2012. Other researchers have shown that it is also possible to remotely take over certain cars. John Markoff, “Researchers Show How a Car’s Electronics Can Be Taken over Remotely,” New York Times, March 9, 2011.
 For background on the incident, see Ali Hashem, “Assassinated Hezbollah leader key to technology, drone operations,” Al-Monitor, December 4, 2013.
 For background, see Scott Petersen, “Downed US Drone: How Iran Caught the ‘Beast,’” Christian Science Monitor, December 9, 2011, and David Cenciotti, “Captured U.S. stealthy drone was hijacked exploiting GPS vulnerability. But hack description does not solve the mystery,” Aviationist, December 15, 2011.
 David Cenciotti, “Captured U.S. stealthy drone in Iran: the simplest solution solves the mystery,” Aviationist, December 19, 2011.
 For background on this product and a video illustrating its use, see http://samy.pl/skyjack/.
 Dan Goodin, “There’s a new way to take down drones, and it doesn’t involve shotguns,” Arstechnica.com, October 26, 2016.
 For a reflection of this issue, see the testimony of German al-Qa`ida recruit Rami Makanesi. Paul Cruickshank, “The Militant Pipeline: Between the Afghanistan-Pakistan Border and the West,” New American Foundation, July 2011, pp. 47-48.
 Muhib al-Jihad al-Akbar, “The Drones: A Very Important Announcement.” See also Adam Rawnsley, “CIA Drone Targeting Tech Revealed, Qaeda Claims,” Wired, July 8, 2009.
 “The Al-Qaida Papers: Drones.”
 Abu `Ubayda `Abdullah al-`Adam, Terrorism Industry: Episode 19, February 2012. Al-Qahtani noted in his “The Dirty UAV” post that “anyone who uses communication devises should be secretly tracked.” He added that “each [drone] strike needs 1-3 spies … because this is the only reason that explains the accuracy of these strikes.”
 Al-`Adam, Terrorism Industry: Episode 19.