Such was the profound effect of the Sept 11, 2001, terrorist attack on the World Trade Center and the Pentagon that it changed many aspects of our lives, especially the way we travel. The attack earned Osama bin Laden instant notoriety and made Al-Qaida synonymous with terrorism. Governments around the world responded with a "global war on terror" led by the United States, and counter-terrorism was propelled to the top of the agenda of many security agencies.

Ten years on, as we approach the 10th anniversary of 9/11 there appears to have been major successes in the war against terrorism. Most significantly, Osama bin Laden was hunted down and killed by US special forces on May 1 this year, and the US Secretary of Defense Leon Panetta has declared that the US was "within reach of strategically defeating Al-Qaida".

While the death of bin Laden cannot be dismissed as an insignificant event, a close examination of terrorist incidents in the past decade suggests that the terrorist threat has evolved beyond Al-Qaida and bin Laden both. Terrorism experts such as Marc Sageman have labeled this trend as the "leaderless jihad", which in essence comprises homegrown and self-radicalized individuals who resort or are committed to terrorism without being actually recruited by Al-Qaida or other established terrorist groups.

The rising trend of "leaderless jihad" can perhaps be best observed from the London bombings of 2005 which targeted the city's transport system. While the initial signs pointed to an Al-Qaida attack, subsequent investigations revealed that the four suicide bombers who perpetrated the attack were British citizens and were not members of Al-Qaida.

In similar vein, the Madrid bombing a year earlier in 2004 was carried out by a group of young men of mostly North African descent who were inspired by but not members of the Al-Qaida. Among numerous speculations pointing to the direct involvement of Al-Qaida, a two-year investigation into the attack concluded that the terrorists were acting on their own rather than at the behest of Al-Qaida.

These two attacks dispel the notion of Al-Qaida being the "headquarters" of international terrorism coordinating terrorist attacks across the world. Rather, post-9/11, in the face of relentless efforts of the international community, it would appear that Al-Qaida has transformed into more of an inspirational rather than operational entity.

It cannot be said, though, that Al-Qaida has been conclusively defeated, and it is clear that its venomous ideology continues to attract impressionable minds from all facets of society all over the world. Therefore, it is imperative that counter-terrorism efforts are not confined to being an Al-Qaida-centered strategy. This brings into focus the challenge posed by self-radicalized individuals.

Perhaps the most well-known example of an individual radicalized by extremist content online would be Younes Tsouli, son of a Moroccan diplomat living in the United Kingdom. Arrested by British authorities in 2005, Tsouli was subsequently found guilty of inciting others to commit terrorist acts by setting up websites with extremist materials. While these websites supported Al-Qaida, it is noteworthy that Tsouli was not an actual member of Al-Qaida but an individual who had become converted to its cause via the Internet.

In 2007, Singapore authorities detained Abdul Basheer Abdul Kader under the Internal Security Act for plotting "militant jihad" with the Taliban in Afghanistan. Alarmingly, the then 28-year-old Abdul Basheer was a well-educated lawyer and a lecturer who became self-radicalized after accessing extremist materials on the Internet. In 2010, another young Singaporean, Muhammad Fadil Abdul Hamid, was detained for similar reasons.

While the above examples relate to radical Islamic terrorism, it is important to note that the concept of a "self-radicalized individual" is not restricted to a particular religion or ideology.

There is no better example to illustrate this point than the terrorist attack in Norway on July 22, in which 77 people, including many teenagers, died. In contrast to the initial knee-jerk response of the media pointing to the possible involvement of Islamic terrorists, the perpetrator of this attack turned out to be a blonde, blue-eyed, homegrown Norwegian named Anders Behring Breivik.

Further investigations revealed that Breivik is a right-wing extremist, strongly opposed to multiculturalism. According to his 1,500-page manifesto uploaded online before the attack, he likened himself to the Knights Templar in a struggle against Muslims and "cultural Marxists", which apparently served as his motive to attack the youth camp organized by the ruling leftist party. This incident, along with that of the 1995 Oklahoma bombing by Timothy McVeigh, is a cautious reminder that the phenomenon of self-radicalized terrorism can occur anywhere along the ideological/religious spectrum.

The threat from self-radicalized individuals poses formidable challenges for security and law enforcement agencies. Given the need to respect civil liberties and privacy in most developed countries, it is undeniable that the monitoring and detection of an increasingly radicalized individual is near impossible. For policymakers engaged in counter-terrorism, it is clearly an easier task to target a tangible and perceptible enemy such as Al-Qaida than to formulate a strategic framework to detect and deal with the issue of self-radicalization.

Ten years after the 9/11 attacks, there have been notable successes and authorities have made inroads in the war against terrorism. However, counter-terrorism strategy has to devised according to the evolving terrorist threat. While it may sound clichd, what is certainly required is to adopt a whole-of-society approach to fight terrorism, with a symbiotic and effective relationship between the government and the community.

For example, the foiled bomb attacks on a Northwest Airlines flight in 2009 and at New York Times Square in 2010 owe greatly to the crucial intervention of the average "Citizen Joe" who helped thwart the attacks before it materialized.

In the final analysis, there is no clear prescription to combat the new threat posed by self-radicalized individuals. The emergence of this form of terrorism may require society to re-examine its very own fabric and ask tough questions. In particular, the entire social and economic structure may have to be looked into to find the seeds of self-radicalization, especially the factors that lead to alienation and disenfranchisement, which invariably form part of the mindset of self-radicalized individuals.

The author is an associate research fellow at the Centre of Excellence for National Security of S. Rajaratnam School of International Studies (RSIS), Nanyang Technological University, Singapore.