16 National Security Strategy and Strategic Defence and Security Review 3.6 A number of Islamist terrorist groups are active across the Middle East, Africa and South Asia, with increasing reach into Europe. The emergence of ISIL and its brand of violent extremism has significantly increased the threat. ISIL now operates over much of Syria and Iraq, and has affiliates in other countries. ISIL has recruited foreign fighters from most countries in Europe and across the Islamic world. Approximately 800 British nationals have travelled to Syria to take part in the conflict since it began, and many have joined ISIL and other terrorist groups. A large proportion were previously unknown to the police and security agencies. Of those who are known to have travelled about half have returned. Some of these, and many of those who remain in Syria, pose a threat to our security. 3.7 Terrorists have tried to use a wide variety of methods of attack, from unsophisticated knife and gun attacks to more complex plans involving firearms and explosives at multiple locations. Terrorists who are directed or inspired by ISIL pose a direct threat to our security and that of our allies, as demonstrated by recent attacks in Paris as well as in the Middle East and North Africa. Our law enforcement and security and intelligence services have stopped at least seven different attempts to attack the UK in the last 12 months alone. Passenger aircraft remain a primary target for some terrorist groups. Some groups, especially ISIL and Al Qa’ida, will also try to acquire chemical, biological and radiological capabilities. 3.8 Extremist and terrorist groups, in particular ISIL, have exploited the internet and social media to distribute large quantities of often sophisticated online propaganda intended to radicalise and recruit large numbers of people here and in other countries. Terrorist groups also use widely available encrypted online communications to plan attacks. This and other attempts to evade detection mean that it is now much harder for the police and security agencies to spot, investigate and then successfully disrupt terrorist attack planning. It is also difficult to investigate and disrupt terrorist and criminal threats when they originate from states which have poor governance, or which lack credible and effective police and security organisations operating to our human rights standards. 3.9 The significant threat posed by terrorist groups makes it all the more important that we invest to tackle this issue head-on at home and abroad using the full spectrum of our capabilities. Northern Ireland related terrorism 3.10 There is still a threat from Northern Ireland related terrorism. Violent dissident republicans have sufficient numbers and weapons to pose an enduring threat in Northern Ireland primarily to the police, but also prison officers, members of the Armed Forces, national infrastructure and commercial targets. Violent dissident republicans aspire to target Great Britain, and some groupings remain capable of conducting one-off attacks, but currently consider Northern Ireland to be their main focus. Impact of instability 3.11 The conflict in Syria and Iraq has shown how crises can trigger and accelerate instability across a region, and the challenges created by state failure or a lack of effective, publicly legitimate and accountable governance. Such challenges include regional instability, large-scale humanitarian need, mass migration and human trafficking, and exploitation of weak governments or ungoverned space by terrorist groups and criminals. Instability overseas also undermines affected countries’ prospects for poverty reduction and economic growth.