Universiteit Leiden Leiden University | Discover the world at Leiden University.

Security and Threat


Combining different disciplines, Leiden University researchers work together to formulate innovative solutions to societal problems. Below is an example from the field of politics and governance.

Overview research dossiers


Fighting against fear

Research is the basis for good security policy. By analysing the motives of radicalised people and identifying the biggest risks in the area of digital communication, Leiden University researchers are helping governments to formulate effective countermeasures.

<p>How can we ensure that citizens continue to feel safe? (photo: Olaf Kraak ANP)</p>

How can we ensure that citizens continue to feel safe? (photo: Olaf Kraak ANP)

Terrorism is a global threat, and Dutch society has not escaped its impact. Attacks like those in Brussels and Nice bring the threat of terrorism very close to our borders. How and why do terrorists carry out attacks? How can we thwart their plans and ensure that citizens continue to feel safe? How do we deal with risks relating to the internet?

Leiden researchers look for answers to these questions. They share their insights with other researchers, with the Dutch and other governments, and with the general public. Thanks to their work, we have a better understanding of terrorists, and governments can offer more effective resistance to the threat that they pose.

For instance, our researchers analyse what motivates ‘foreign fighters’ to go to war zones. Research into their reasons and their social environment can help to prevent this. They also look at ways to discourage radicalisation during and after detention: How can this be achieved? Another aspect of security is the protection of digital communication: How can you make it secure, and what legal frameworks are involved?

Never 100% safe

Researchers and policy makers do their best to improve security, but there’s no such thing as ‘100% safety’. Bibi van den Berg, researcher in the field of cyber security, says: “The world has never been a safe place, but in the past people were much more at the mercy of fate. Things sometimes just happened to you. Technology has allowed us to reduce the influence of fate. Our lives are now so safe and secure that we no longer accept danger. As a society, it’s very important to realise that we can’t completely prevent bad things happening.”

More information:

Institute of Security and Global Affairs
Cyber Security Academy The Hague
Faculty of Governance and Global Affairs

Foreign fighters

Understanding what motivates foreign fighters to go and fight in war zones and analysing their social environment offers a basis for preventing them from going.

The number of young Dutch people travelling to Syria to join the fighting has increased considerably since 2013. This is worrying, because these ‘foreign fighters’ return with combat training and a radicalised ideology. These fighters are the subject of research conducted by Edwin Bakker, Professor of Terrorism and Counterterrorism, for the Dutch government and also in the context of the EU. How dangerous are they, and what can we do to limit the potential risk? In order to address these questions,

Foreign fighters

he and his colleagues collected all the existing information on European foreign fighters. They also spoke in person to fighters who have returned to the Netherlands, and to the families of young people who have left or wanted to leave. There are currently (autumn 2015, ed.) more than 4,000 European foreign fighters, over 200 from the Netherlands, a few hundred from Belgium and around 1,000 from England and France.

Attractive career move

Bakker: “Young people have very different reasons to go and fight, ranging from conviction (they see it as a basic duty of their religion, like visiting Mecca) to imitating the behaviour of others ('my best friend went too') and from genuinely wanting to help to trying to give meaning to their lives. Some of these young people have problems here at home, possibly with money, their studies or the police. Then they hear about the possibility of leaving. Within one-and-a-half day’s travel, they are suddenly fighters who have been ‘called to protect families under the holy flag of Islam’. Which is, of course, an attractive career move.”


Foreign fighters who have returned are a potential threat because some of them come back traumatised or radicalised, and may resort to violence. American research into incidents among veterans of the wars in Iraq and Afghanistan shows that they suffer from post-traumatic stress disorder as a result of the horrors they have witnessed. “It is extremely likely that fighters will experience atrocities in Syria. What’s more, soldiers know that they will come up against these kinds of intense situations, whereas young people who go and fight are completely unprepared. This lack of preparation is asking for trouble. There’s a big risk of psychological problems, either there or when they return.”

Important role for mothers

“If you want to prevent young people travelling to Syria, parents – and mothers in particular – have an important role to play. What the government can do is to increase awareness of the phenomenon and give those involved (parents, teachers, social workers) some idea of the process that can lead to a trip to Syria or Iraq, so that they can recognise the signs and phone the police or a newly set up radicalisation helpline if they suspect that this may be happening.”

Arrest, detention and release of jihadists

People who are arrested on suspicion of preparing an attack are at risk of becoming radicalised either during or after their detention. Whether or not to arrest someone requires careful consideration. At the end of the prison sentence, it is important to provide effective supervision of the reintegration process.

Since the 11 September attacks, laws have been passed around the world, and also in the Netherlands, which make it easier to arrest people who are suspected of preparing an attack. This results in more arrests, but also in a greater risk of the suspects becoming radicalised. 

The perpetrators of the Charlie Hebdo attack and the Toulouse shooter all had a criminal history and were radicalised in prison. How can you prevent the further radicalisation of jihadists or suspected jihadists in prison or after their release?

Daan Weggemans en Beatrice de Graaf in talkshow Pauw (video in Dutch)

With this question in mind, the Leiden University terrorism experts Daan Weggemans and Beatrice de Graaf (Utrecht University, formerly of Leiden University) conducted an exploratory study of the process surrounding the arrest, detention and release of jihadists in the Netherlands. Since the heavily guarded terrorism wing of the prison in Vught was opened in 2006, it has held more than 80 prisoners; some for just two weeks, others for a couple of years. For their research, Weggemans and De Graaf spoke with detainees, former detainees, police officers and various professional care workers about their experiences.

Difficult judgement

How does a prisoner end up in a terrorism wing? Weggemans: “It happens when you’re accused of a terrorism-related offence. That could be preparing an attack or providing financial support to certain organisations. The problem for the government is that this always involves a difficult judgement about whether someone constitutes a real threat and is actually guilty. In any case, many of those accused are ultimately not convicted because they’re found to be innocent or there’s insufficient evidence.”

More resentment

Whether to arrest someone or not is an important question, because prison can either lead detainees to abandon their extreme views or can actually radicalise them. “Some people develop more resentment precisely because they’ve been arrested, or find confirmation of their ideological views through contact with other detainees. But discussing things with others can also make people give up their extreme ideology. Every case is different, and the professionals and institutions in-

Prison can either lead detainees to abandon their extreme views or can actually radicalise them

Prison can either lead detainees to abandon their extreme views or can actually radicalise them

volved will always have to weigh up both sides when developing policy.”

Successful reintegration

At the end of the prison sentence, successful reintegration into society is crucial for long-term security. “It’s still too early to draw firm conclusions,” says Weggemans. “But three important recommendations have emerged from the interviews that we conducted. First: encourage former detainees to have contact with (non-radicalised) family and friends, or to make new social contacts, for instance through a sports club. One way to do this is to find them somewhere to live that is close to those social contacts. A second factor: help them with practical matters, such as finding a job. And a third recommendation is to make sure that former detainees have contact with experts who can assess how they’re getting along, or who can help them.”


Weggemans and De Graaf see that there are particular measures that make the reintegration process more difficult. “First, the fact that you’ve been arrested creates a stigma that’s very hard to shake off,” begins Weggemans. “And that makes it difficult to find a job, for instance. On top of that, some detainees are put on an international UN terrorist list after their release, whether they were found guilty or not. That has some very serious consequences, including the freezing of your assets. Even if you have a job and earn a salary, you can’t use your bank card. And some former detainees just say they don’t want to integrate. And as a society there’s not much you can do about that, apart from monitor them.”

In addition to the reintegration of jihadists, Weggemans also researches the reintegration process of politically sensitive prisoners, such as serious violent or sexual offenders.

The impact of terrorism and crisis communication

A cautious response to a crisis or terrorist act avoids the creation of a culture of fear. This is another way to reduce our vulnerability to terrorism.

Why are we so vulnerable to terrorism if the likelihood of it happening is so small? “The fear of an act of terrorism can be a very powerful weapon,” says Edwin Bakker. “Society and governments have to ensure that the spread of panic is kept to a minimum.”
In countries that live in constant fear of an attack, terrorists are in effect already successful without having to take any action. There are therefore two important aspects of counterterrorism:

Protest in Luxembourg after the attack on the Charlie Hebdo editorial team (photo: Wikipedia Commons)

Protest in Luxembourg after the attack on the Charlie Hebdo editorial team (photo: Wikipedia Commons)

doing everything possible to reduce the likelihood of a terrorist attack, and managing unease and fear in the population. In recent years, more attention has been focused on the second of these two aspects. The reason for this is the growing realisation that fear and unease promote discrimination and polarisation, and can even lead to radicalisation and thus to more terrorism. The government has an important role in limiting the culture of fear.

Risk society

This culture of fear can easily arise today, says Bakker. “We live in a changing society that is no longer very good at dealing with risks, what is known as a risk society. This makes us more vulnerable to terrorism. In the Netherlands at times we definitely go way over the top in our approach to risk limitation. If there’s an incident, the response from politicians is often: 'This must never happen again’. But a hundred percent safety and security is an illusion, because it’s just not possible for us to prevent everything. Perhaps governments and politicians should emphasise this more often, and display more resilience.”


“Politicians have an important role in increasing or reducing fear. We in the Netherlands responded very badly once in the past, after the attack on Theo van Gogh. Although this was a matter of one single man who had killed another, the deputy Prime Minister, in answer to a question from a journalist, called it ‘war’. He therefore gave the impression that one person could start a war in a country. You then give the perpetrator an enormous amount of power, and you make it attractive for others to come up with something similar.”


“We also responded very well once, on Queen’s Day in Apeldoorn in 2009. It was a terrible event: a planned attack on the head of state. If you watch the footage, you feel the terror all over again. But who still remembers the perpetrator’s last words? Hardly anyone. The whole day ran very smoothly after the attack. The word terrorist was hardly mentioned at all. In short, it was dealt with very well.”

Speech by mayour Aboutaleb after the attack on the Charlie Hebdo editorial team (photo: ANP)

Speech by mayour Aboutaleb after the attack on the Charlie Hebdo editorial team (photo: ANP)

Basis for policy and protocols

“For governments, we collected examples of good and bad responses to acts of terrorism. We also included the best examples of crisis communication. We provided them with a basis upon which they can formulate policy and protocols.” The future focus of Bakker’s research will be on specific strategies for governments to make societies more resilient to terrorism. In addition, he and his colleagues

at the Institute of Security and Global Affairs also look at crisis communication more broadly. For instance, Ruth Prins has conducted research on the role of mayors with regard to security and crisis situations, and how they communicate about them. As politicians who are very close to the country’s citizens, they are tremendously important when it comes to creating a stronger sense of safety.

Cyber security

To make digital communication more secure, we need to tighten up the legal frameworks and identify the biggest cyber threats.

Digital technology features more and more in the lives of citizens and consumers, and in the functioning of companies and the government. Cyber security, the guarantee of security in the use of digital technologies, is therefore becoming increasingly important. Not only technological, but also organisational, economic, legal and administrative aspects have a prominent role. It is unimaginable what could happen if malicious hackers managed to get into systems of critical infrastructures, such as Schiphol or the Port of Rotterdam. Leiden University senior lecturer Bibi van den Berg conducts research on the security of Dutch and international digital communication and possible ways to improve that security.

One of the main focuses in Van den Berg’s research is the division of responsibilities in the area of cyber security between governments, national and international institutions, companies and end users themselves.

What would happen if malicious hackers managed to get into systems of the Port of Rotterdam

What would happen if malicious hackers managed to get into systems of the Port of Rotterdam

For this purpose, she reassesses current theories in the field of regulation and ICT by applying them to this new domain. She also evaluates existing regulation strategies, such as the application of law and other rules or the use of economic incentives, in the light of problems that arise in relation to cyber security.

What is cyber security?

Van den Berg first researches the fundamental questions: What exactly is cyber security, and how big would the problem be if digital security was breached? “We still know far too little about the concept,” she says. “Firstly, because the parties concerned all have a different focus of attention. When you mention cyber security to private individuals, they think about the protection of banking details. If you ask the police, they will say that their cyber security focuses on hackers and terrorists. Ask the army, and they will say that it’s about cyber warfare (waging war by digital means). When you speak to politicians about this topic, they think of privacy problems and also of national security. This makes it very difficult for governments to decide what the focus of cyber security policy should be.”

If Schiphol airport would be hacked, this could have major consequences in terms of economic damage but also in terms and physical safety of citizens.

If Schiphol airport would be hacked, this could have major consequences in terms of economic damage but also in terms and physical safety of citizens.

Cyber Pearl Harbour

As well as uncertainty about the definition, not much can be said about the actual threat in the area of cyber security. “Curt Weldon, the chairman of a subcommittee of the National Security Committee in the United States said a few years ago that it was just a matter of time before there was a cyber Pearl Harbour (in America), but in fact nothing has happened yet. There have been no cyber attacks resulting in large-scale disruption, and we have very few figures to interpret.”

One of the sectors where cyber incidents could have the greatest impact, says Van den Berg, is in the domain known as ‘critical infrastructures’, such as ports, power stations, dykes, airports, and so on. If elements of those critical infrastructures are hacked, this could have major consequences, not only in terms of economic damage but also in terms of the physical safety of citizens. Protection of those systems is not just a matter of purely technical maintenance; it also involves monitoring the interaction between users and technologies. “Hackers look for ways to use systems for their own purposes, for ways to exploit technological possibilities and to get around technological impossibilities. Sometimes a system becomes vulnerable because it is ‘accidentally’ used by people in the wrong way. Think of users who share vast quantities of sensitive data by mistake, or put a malware-infected USB stick into a computer containing commercially sensitive information.”

Digital signposting

Another part of Van den Berg’s research focuses on raising public awareness about the use of digital media. “Do you know exactly what happens when you open a website or upload a photo? A lot of people don’t realise what they’re doing when they’re on the internet, although they really should be aware of it. At the same time, of course, organisations also have a responsibility to provide the public with proper assistance and information concerning the use of sites. I research the best ways to help citizens with internet communication, and how their behaviour is regulated, by means of both the law and digital signposting and barriers.”

What are specific examples of digital barriers? “They include the use of filters and blocking of child porn on the internet. Or preventing access to peer-to-peer networks for file sharing. But also the use of parental controls by parents who don’t want their children to see YouTube content that’s unsuitable for their age. These are all measures that make it technically impossible (or at least very difficult) to engage in certain behaviours on the internet. Measures of this kind are used on a large scale,

An example of 'parental control'

An example of 'parental control'

by both the private sector and the government, but there’s very little knowledge about them, let alone public debate. For example, about their ethical and legal limits.”

Shortage of professionals

Together with other experts in the research field and the private sector, Bibi van den Berg is a member of the Cyber Security Council, which advises the government on policy in the area of cyber security. A recent recommendation was to invest in the teaching of cyber security. “The Netherlands has only a handful of experts, and they don’t have enough time to train people. There’s a shortage of lecturers and instructors, while companies and governments are desperate for professionals who can help with digital security.”


Leiden scientists working in this research area

  • Prof. dr. Edwin Bakker
  • Dr. Bibi van den Berg
  • Drs. Jelle van Buuren
  • Mr.dr. Quirine Eijkman
  • Dr. Elke Devroe
  • Liesbeth van der Heide MA
  • Drs. Constant Hijzen
  • Prof.dr. Joanne van der Leun
  • Mr.dr. Jan-Peter Loof
  • Prof.dr. mr. Erwin Muller
  • Dr. Ruth Prins
  • Bart Schuurman MA
  • Daan Weggemans MSc
  • Prof.dr.mr. Maartje van der Woude
  • Jeanine de Roy van Zuijdewijn MA

Prof. dr. Edwin BakkerProfessor of Terrorism and Counterterrorism

Topics: Radicalisation, jihad terrorism, fear of terrorism, counterterrorism

+31 (0)70 800 9506

Dr. Bibi van den BergSenior University Lecturer

Topics: Cyber security, internet regulation, privacy & identity, techno-regulation and nudging, robotics & artificial intelligence

+31 (0)71 527 2834

Drs. Jelle van BuurenPhD Candidate

Topics: Lone Actor Violence & Terrorism, (counter) terrorism, conspiracies, legitimacy & violence, European internal security cooperation, intelligence, protest movements

+31 (0)70 800 9506

Mr.dr. Quirine EijkmanResearcher

Topics: human rights, rule of law, privacy, national security, surveillance

+31 (0)70 800 9573

Dr. Elke DevroeAssociate Professor

Topics: Police, plural policing, governance of social disorder, urban crime, incivilities

+31 (0)70 800 9375

Liesbeth van der Heide MAEducation and Research Staff Member

Topics: De-radicalisation / re-integration of terrorists, prisons, impact of terror threat and countermeasures, terrorism law suits

+31 (0)70 800 9517

Drs. Constant HijzenPhD Candidate

Topics: Contemporary history (post-1945), intelligence studies, safety culture, intelligence and security services

+31 (0)70 800 9506

Prof.dr. Joanne van der LeunProfessor of Criminology

Topics: Crime policies, human trafficking, public order and safety, immigrant policies

+31 (0)71 527 7522

Mr.dr. Jan-Peter LoofUniversity Lecturer

Topics: Law, freedom of religion, freedom of speech, public order and safety, terrorism

+31 (0)71 527 7711

Prof.dr. mr. Erwin MullerProfessor of Safety, Security and Law

Topics: Law enforcement, terrorism, safety policies

+31 (0)71 527 7364

Dr. Ruth PrinsAssistant Professor

Topics: Mayors, integral safety policy, (national) police, administrative approach to organised crime, crisis management

+31 (0)70 800 9464

Bart Schuurman MAResearch Staff Member

Topics: Jihadist terrorism, Hofstad group, Clausewitz (military) theory, asymmetrical conflict & strong-power defeats

+31 (0)70 800 9347

Daan Weggemans MScPhD Candidate

Topics: Radicalisation, de-radicalisation, Breivik, frontline workers and extremism, re-integration, terrorism

+31 (0)70 800 9487

Prof.dr.mr. Maartje van der WoudeSenior University Lecturer

Topics: Crimmigration, public order and safety, substantive criminal law, terrorism law

+31 (0)71 527 7552

Jeanine de Roy van Zuijdewijn MAResearch Staff Member

Topics: Foreign fighters, lone actor terrorism, Libya

+31 (0)70 800 9328


Programmes in the Dutch heart of governance and security management

The Faculty of Governance and Global Affairs offers a wide range of study programmes in the area ofnational and international security and governance. The Faculty is situated in The Hague, the administrative capital of the Netherlands and location of the International Criminal Court and over a hundred other international institutions and organisations. Students regularly come into contact with professional practice; for instance, the National Coordinator for Security and Counterterrorism makes time to give talks to students, and many students do internships with governmental and non-governmental organisations in The Hague. The teaching also has a major international impact: more than 100,000 people have followed the Massive Online Open Course (MOOC) on Terrorism and Counterterrorism, for example, and the master’s programme in Crisis and Security Management attracts many international students.

Outreach & News

The outreach of our research extends far beyond the academic world. Our experts often provide media commentary and share their knowledge online. They also make regular appearances as guest speakers at congresses and discussion forums that are open to the general public.