Who are they, and what do they want? Here are six things to know about the members of the insurgent terrorist group.
1. They began as a peaceful group but later radicalized and are intent on overthrowing the Nigerian government.
Founded in 2002 by the Muslim cleric Mohammed Yusuf, the group "started very much as a small, initially peaceful utopian community," Darren Kew, an associate professor at the University of Massachusetts-Boston who has studied the conflict, tells PEOPLE.
The group later radicalized and went underground in 2009 after its founder was killed, setting up something akin to a Taliban state, with assistance from Al Qaeda and affiliate groups. The group was born and remains active in the poorest part of Nigeria, where it blames the problems on corruption and the inability of previous governments to provides goods and services.
"They've got a very idiosyncratic perspective. They are not in step with mainstream Islam by any stretch of the imagination," says Kew. "The core of their message is that this corrupt Nigerian state is the problem. The solution is their vision of an utopian Islamist state."
2. Their current leader, Abubakar Shekau, is radical and ruthless.
Relatively little is known about Shekau, who delegates much of the group's operational duties to subordinates and appears only in occasional videotaped messages, where he mocks the Nigerian military.
Believed to be between 38 and 49 years old, he is a multilingual religious scholar, and is described by CNN as "a loner and a master of disguise." He is seen as more radical and ruthless than Yusuf ever was, and has regularly targeted civilians in the group's attacks. The U.S. is offering a $7 million bounty for information leading to his whereabouts.
3. They believe education for women is evil.
The kidnapping of the Nigerian girls is emblematic of a central opposition to education for women. "They are particularly critical of the Nigerian elite, which they see as Western-educated, too Westernized," says Kew. "They see the secular education system in Nigeria as the vanguard of this Westernized style of life, which they see as forbidden, as sinful, as the root of Nigeria's problems."
"It's within that context that girls being educated in any sort of educational system is an evil that needs to be rooted out. In their twisted logic, marrying them off to their fighters is putting them back on the right path."
4. They could very well make good on their promise to sell the kidnapped girls.
"The selling into slavery is particularly medieval … This is essentially a 'spoils of war' prerogative," says Kew. And indeed, the group's vow to sell the girls isn't just empty bravado – human trafficking is a major problem all across West Africa.
Benjamin N. Lawrance, a professor at the Rochester Institute of Technology, tells The New York Times that if he were to visit any number of West African countries today, "I would have no difficulty, within a matter of hours, in finding a place to procure children."
Sunday Alamba / AP
The group appears emboldened by its new notoriety. Just on Thursday, it launched a bloody assault in Lagos, opening fire on a crowded marketplace and killing more than 300 people, reports the Associated Press.
"Shekau threatened the U.S. in a recent message, but I think it is highly unlikely they will be able to do anything about it for some time. They are nearly entirely absorbed with their goals in Nigeria at present," Kew, of the University of Massachusetts-Boston, tells PEOPLE.
To that end, Nigeria President Goodluck Jonathan said in a speech Thursday, "I believe that the kidnap of these girls will be the beginning of the end of terror in Nigeria." He also thanked the U.S., the U.K., France and now China for their offers of help to rescue those abducted.
the international community is beginning to mobilize against the group in the wake of the shocking kidnappings. President Obama had said this week that the U.S. and its allies are working "to do everything we can to recover these young ladies," and American personnel skilled in areas like intelligence, hostage negotiating and victim assistance are already on their way to the country.
6. Rescue of the girls could be difficult, at best.
Warns Darren Kew, "I think it is going to be very difficult to rescue them all, or even the majority of them. There is some speculation that the girls have been broken into smaller groups and spread around Boko Haram's core area of operations, including over the border into Cameroon, Chad and Niger, where it will be even more difficult to find them."
He adds, "Some of the girls may be ransomed in order to get more funding for Boko Haram, and others may be used at this moment as human shields to prevent the Nigerian air force from attacking Boko Haram locations."
The most optimistic scenario, he says, "may be if Boko Haram is willing to trade some of the girls for the release of jailed Boko Haram fighters and supporters. Government forces may be able to free some of the captives if operations get underway, but kidnappers have killed their captives during some previous efforts to free hostages in Northern Nigeria, so this risk remains as well."
He acknowledges this is "not a very optimistic picture, and I hope I am wrong about it."