Anders Behring Breivik, 32, is handsome, green-eyed, and blond—in other words, not a stereotypical terrorist. His good looks worked to his advantage, helping him gain access to the island of Utoya and allowing him to kill scores of people in one of the bloodiest attacks in Norwegian history. The assault that he carried out on Friday was not only horrific; it also exposed a weakness in counterterrorism strategy in Europe and the United States. The commonly held notion of who a terrorist is means people may lower their guard around Breivik and others who look not Arab, but Western, and the results can be devastating.

“Terrorism is theater,” as security analyst Brian M. Jenkins wrote, and in popular lore the cast is made up of young Middle Easterners. Indeed, many Americans expect terrorists to look like the bearded thugs who made life difficult for Jack Bauer in Fox’s show 24. To be sure, the biggest threat to national security comes from radicals who are affiliated with organizations such as al Qaeda and the Africa-based Islamist group Al Shabab, and these individuals may in some ways look like the television thugs. Yet as the Norwegians found out this week, non–Arabic speakers who have no ties with an Islamist extremist group can also inflict damage on a colossal scale.

The United States has its own experiences with domestic terrorism, and yet stereotypes persist in this country, clouding the views of ordinary citizens and of law-enforcement officials. In February 2010, for example, a computer engineer, Andrew Joseph Stack III, flew an airplane into an IRS building in Austin, Texas, killing one person. He left behind a note that showed he was unhappy with tax laws, and in this way he was attempting to use violence to achieve a political outcome. Yet FBI officials chose not to describe him as a terrorist; instead, they handled the case as a criminal matter.

Many experts believe that the FBI’s assessment was based on the color of Stack’s skin (white) and on his non-Arabic-sounding name, rather than on the facts of the case. In other words, he had carried out an act of political violence, but officials refused to recognize him in this way because he did not fit their idea of what a terrorist looks like.

Perhaps not surprisingly, leaders of international extremist groups are now looking for these types of individuals to carry out future attacks. Anwar al-Awlaki, a radical Muslim cleric who lives in Yemen, and other writers for an English-language Qaeda magazine, Inspire, have been encouraging readers to act independently and to come up with terrorist plots in their own countries.

“He is saying, ‘Look, you may be sympathetic to the movement, but don’t come to Yemen. Just do it on your own,’” says Jessica Stern, the author of Terror in the Name of God: Why Religious Militants Kill. “He and his henchmen have figured out that it’s very hard to find a neo-Nazi, a lone Islamist terrorist, or any kind of lone wolf, because they’re not talking to anyone.”

Unfortunately, popular notions about terrorism may blind people to what political violence is, as in the case of Stack in Austin, and may also make it harder to recognize someone who is preparing to carry out an act of violence. Author Ken Ballen interviewed more than 100 extremists in Indonesia, Pakistan, and other countries for his forthcoming book, Terrorists in Love: The Real Lives of Islamic Radicals, and he found that the vast majority “are not psychopaths or criminally insane.” Instead, as he discovered, “these people know exactly what they are doing, and they believe they’re doing the right thing.”

It is easier to see terrorists as the Other, as someone who holds bizarre views, lives in a far-flung country, and is utterly alien. Yet real-life terrorists are not the shadowy figures of 24; they are just like us. They come from a variety of backgrounds and hold an array of views, but they are clear-headed about their actions and, however misguided, have the courage of their convictions. That, combined with their utterly savage behavior, is what makes them terrorists, not their faith, appearance, or ethnic background, and is also what makes them such an insidious threat.