In a time of terrorism, the enemy within is the most pernicious.

He is the terrorist who can strike at any time. He is the good neighbor who harbors hate. He is he loner who craves to be part of something larger than his own life promises.

Most disturbingly, he is probably a third or fourth generation immigrant.

He is the lethal misfit.

He is also the unique product of the modern world: The immigrant who doesn’t assimilate into the society in which he lives, but connects with the world of his ancestors through technology. He may be a Nigerian youth living in London, Madrid, or Houston, but in his mind he lives in Nigeria because technology makes it possible to do so.

Britain is filled with pockets of immigrants who choose not to assimilate, enjoy the privileges of British society, and deny their nationality.

A few years ago I met a young woman in Doha, Qatar, who covered her head with a scarf and spoke with an English accent.

“Oh, you’re English,” I said, thinking we might talk about the old country.

Stiffly, she said, “I was born there, but I am an Arab.”

Before taking a job with Al Jazeera’s Web site in Doha, she had never been out of England. But psychologically, she had grown up in the Middle East and was indifferent to the culture and the people who had taken in her family and educated her with tax money. She closed her ears in school and opened them in her local mosque. She is typical of immigrant children from Houston to Rome and from Toronto to Sydney, alienated by their own intent, angry and vulnerable.

When America’s immigrants were pouring in through Ellis Island, N.Y., they were coming to a new life; and however hard, it was going to be an American life. Sentimentally, they might sing rebel Irish songs in Boston, dance the polka in St. Paul, Minn., and mix the marinara sauce in Hoboken, N.J., but the tickets that brought them here were one-way tickets. The only contact with the world they had left was by slow, sea-borne letters.

Now, with technology, all immigrants’ tickets to America are essentially roundtrip tickets. Immigrants no longer have to consider assimilation as a worthy or a necessary goal.

There are reasons of national unity to work against the Balkanization of America. However, the clear and present danger is from those likely to fall prey to the malicious excesses of politics or religion.

It is frightening that a wealthy young man from Nigeria, Umar Farouk Abdulmuttalab, tried to blow up an inbound airliner on Christmas Day. But the home-grown rebel–like the five, middle-class young men who are now being held in Pakistan–is more concerning.

Gradually, screening of passengers will improve and the intelligence community will handle information better. In the meantime what are we, and other nations like Britain, to do about our citizens who hate the lands that have given them so much? Spy on our neighbors? Inform on our friends?

If we do those things, the enemy within will have won; and if we don’t, the enemy within may win with an act of terrorism. –For the Hearst-New York Times Syndicate