Despite the natural apprehension, we must not interpret a statistically insignificant number of cases as evidence for the magnitude of the problem of radicalization among Muslim Americans. Such a generalization will cause injustice to a large group of people and might also adversely affect the goal of reducing the alienation of Muslim youth.

We need a calibrated approach that takes the social and economic needs of the community into account and work with the community leaders. And we need to be realistic about the overall enterprise: the same way we will never be able to address all the factors that drive some young people to crime we will never be able to address the diverse factors that lead particular individuals to terrorism.

Unfortunately, we must also accept that eventually some will succeed in carrying out attacks. Such attacks will not be on the level of 9/11 but more on the scale of the London bombing.

Even more likely are attacks by lone gunners like Nidal Hassan. Troubling as such events are, they do not have inherent strategic value. Fortunately, while the Internet provides important information for would-be terrorists, it is not a sufficient substitution for formal training, thus limiting considerably the kind of attacks homegrown terrorists can carry out.

Those who do seek training abroad are often identified through effective intelligence work. In fact, if there is one silver lining in the wave of threats, it is that the F.B.I. and the C.I.A. are getting better at their jobs and are able to expose threats relatively early on. This is not a substitution for a more comprehensive anti-radicalization effort, but it is a considerable achievement.

They sought something more, something true and they stumbled upon a radical ideology that provided them with easy answers. The 2007 New York Police Department report on radicalization calls this the “indoctrination phase” where the individuals intensify their beliefs and conclude that “the conditions and circumstance exist where action is required to support and further their cause.” From there, it can be a short step to violent action.

Before the Internet, only those living in hotbeds of radicalization in Saudi Arabia, Egypt or Pakistan had access to these ideas. Now, anyone can point and click their way to a radical Web site.

This is not to say that anyone who views a jihadi video will magically become radicalized. But it is the case that, if you are open to the message, it is there in abundance. Jihadi chatrooms and blogs provide echo chambers and build a self-reinforcing community of the likeminded.

The case of Jihad Jane reveals that violent Islamic extremism is not about religion or ethnicity, but rather it is an ideology that can affect anyone with access to the Internet and a mindset susceptible to that argument.

We have to sever the links between intermediaries and their recruits. Partnerships between federal and local law enforcement agencies — like Joint Terrorism Task Forces — are helping to uncover domestic plots. The Department of Homeland Security, through its office for Civil Rights and Civil Liberties, has looked to increase official engagement with Muslim communities.

This is an important initiative, because the family and friends of suspected criminals often are the best resources for law enforcement officials. The families of the “Northern Virginia Five,” for example, alerted authorities when the young men went missing last November.

To date, though, the government lacks a comprehensive framework for addressing Internet radicalization. Developing one will be necessary to curb the influence of intermediaries, especially those who use email, chat rooms, YouTube, Facebook, and other social media to attract would-be extremists.

On a broader level, policymakers need to think more aggressively about ways to counteract al-Qaeda’s “West vs. Islam” narrative. The Obama administration has rightly discarded phrases like “war on radical Islam” that proved divisive during the early, post-9/11 years. But officials also should do more to highlight victims of terrorism, who are overwhelmingly Muslim, as a way to “de-glorify” jihad. The government must also continue to support and promote Muslim American community leaders who speak out against violence.

Third, while they lack the ability to hit so-called “hard” targets decisively, they are perfectly able to attack the plethora of “soft” venues that abound, like shopping malls, cinemas, mass surface transportation, restaurants and office complexes.

Fourth, in the cases of religious “converts” the desire to contemplate extreme violence is likely to be especially strong as this may well be viewed as the most visible way of demonstrating and validating their Islamist credentials. Finally, they can greatly inflate the perceived threat of militant extremism because their actions are specifically directed against places central to day-to-day lives of ordinary citizens.

One of the main factors serving to encourage the growth of homegrown terrorism is the Internet. The number of active extremist Web sites around the world has exploded over the last several years and by 2006 was thought to number around 5,000.

These forums not only provide a readily accessible virtual platform through which to disseminate extremist propaganda, in so doing they also act as a highly powerful means for self-radicalization. And as cases in the U.S. show, the audiences for these sites are not necessarily Muslims.

What does all this mean for future threat containment? A trend toward homegrown terrorism should presumably reduce strategic attacks against iconic targets and venues. But locally radicalized individuals will provide al-Qaeda and associated movements with an amorphous cadre of militants that can be used to show that the transnational terror threat is one that exists in all places at all times.