The main target in local level online propaganda is young Islamic males, who are susceptible to manipulation and radicalization by extremist Islamic preachers, especially in social media platforms. In (Passy 2001) is stated that social networks play an important role in influencing the behaviour of individuals and their willingness to take part in collective action because of their socializing, recruitment and decision shaping functions. The benefits conveyed by the spiritual leaders for involvement in terrorism are, amongst other things, a sense of belonging to a strong collective identity, status, or power. They promote common knowledge of terrorism ideologies and violence and generate support for their cause within the Muslim communities, e.g. by exaggerating the external threats from other groups (the political and moral decay of the U.S.) (Chatfield, Reddick and Brajawidagda 2015). Adam Yahiye Gadahn, 25-year-old U.S. citizen, converted to Islam at the age of 17 and adopted increasingly radical political views through the close associations with radical Islamic spiritual leaders, was recruited by Al-Qaeda and later became active on YouTube as a leading voice of AsSahab, al-Qaedas media arm, with violent threats against Americans on streets. By establishing an emotional connection with the targeted audience, terrorist propagandists are able to recruit new terrorists and raise money for jihad. Al Qaeda, for example, always depended heavily on donations, and its global fundraising network is built upon a foundation of charities, nongovernmental organizations, and other financial institutions that use websites and Internet-based chat rooms and forums.

On a global level, terrorists use propaganda to spread disinformation and attack governments to provoke a counterterrorism response. Social media platforms are used to disseminate horrific images and other violent content. The main goal is to intimidate Western public opinion and to support the moral legitimacy of terrorism violence, e.g. by reframing suicide attacks as martyrdom operations.

Terrorists are able to deliver threats, such as Cyberfear (TN 2017), which is generated when terrorists threat to pose a computer attack by pretending to be able to, for example, bringing down airliners by disabling air traffic control systems, or disrupting national economies by wrecking the computerized systems that regulate stock markets, until the public believes that an attack will happen.

Many social media websites have policies against content in support of terrorism or violence, but influencers can just open new accounts in case of deletion of their profiles. Prevention of propaganda and the spreading of extremist beliefs is a difficult subject, because it can easily lead to the restriction of free speech and the internet as a place of free expression. To ensure the safety of the population and protection against radical ideas and extremist manipulation, the mechanisms and actions of terrorist propaganda have to be fully understood and examined first in order to find countermeasures.

Sharing information on how to detect manipulation of terrorists and the urge to being cautious will not have a great impact on those who are vulnerable to psychological manipulation by spiritual leaders and the promise of belonging to a group which is sharing the same interests and goals. The solution is therefore to monitor, classify and analyze terrorist communication over online mediums in order to prevent further attacks and investigate crimes. The main objective is to identify radicalized individuals and rehabilitate them into the society. In particular, such prevention approach can be actuated by:

• Monitoring extremist behavior on social media. Monitoring the opinions and sentiments of the users of online social networks, like examining the history of interaction with social media such as liked Facebook pages and persons of interest can help design better counter-terrorism mechanisms and policies. Unfortunately, it is very easy for terrorists to manipulate their data by providing false information which can make this technique error-prone and unreliable. Additionally, it is possible to analyze the social network of suspicious persons by identifying explicit links between them and terrorist groups. This is useful when more than one person is involved and when we already know some of the participants. If the attacker is known, it is possible to use facial recognition on online available images or videos of this person and identify other suspects in these mediums, as well as tagging the uploader of these contents as likely to be a terrorist sympathizer.
• Keyword- and feature-based analysis of communication. Data mining offers the possibility to evaluate twitter, dark web forums and other communication mediums according to the use of certain keywords for prevention of attacks and radicalization. Extremists use online communication as mentioned earlier for recruiting, ideology sharing, radicalization and the planning of attack. Possible keywords are terror, jihad, dirty bomb, biological weapon and so one (Mahmood 2012). Keyword-based flagging is used by the US Department of Homeland Security to monitor online social networks. Another way to analyze terrorist communication is to identify the author and formulate an author profile containing information about gender and education, based on their writing style as proposed in (Abbasi and Chen 2005). Greetings, signatures, quotes, links and forum messages are used to automatically extract linguistic features and evaluating stylistic details for patterns of certain authors which are linked to extremist content. Noisy data, however, generates a large number of false alarms. Attackers can easily circumvent the monitoring system by misspellings or abbreviations, or using own code words which the law enforcement agencies are not familiar with.
• Honeypots. Intelligence agents can infiltrate extremist chat rooms or forums posing as radicals, pretending to have the same violent desires and interests shared in terrorist groups, which is tempting terrorists to reveal themselves. Then they can work on dissuading the radicals from resorting to violence. While extremists would not care to the calls for peace in the Middle East, they might listen to religious arguments about the nature of jihad. This process involves waiting for someone to fall into the trap, which is most likely not happening with well-trained terrorists or careful lone attackers.
• Shut down terrorist websites. A new strategy by the U.S. government was announced in 2007 to create a blacklist of violent and terrorist-related web sites. This blacklist should be enforced within the public sector, so that computers in schools, libraries and universities would be prevented from accessing blacklisted sites. The Counter Terrorism Internet Referral Unit (CTIRU) is currently in charge of website blocking which established in 2010 to assess internet content and coordinate removal of inappropriate content.