Boko Haram's lethality is indisputable.
The militant group has bombed schools, churches and mosques; kidnapped women and children; and assassinated politicians and religious leaders alike.
It made headlines again this week with the abduction of more than 100 schoolgirls in the town of Chibok in northeastern Nigeria. After a fierce gunbattle with soldiers, the militants herded the girls out of bed and onto buses, and sped off. Only a few of the 129 girls have been freed.
What exactly is Boko Haram, and why has it turned into a Nigerian synonym for fear and bloodshed?
What does 'Boko Haram' mean?
The name translates to "Western education is sin" in the local Hausa language.
The militant group says its aim is to impose a stricter enforcement of Sharia law across Africa's most populous nation, which is split between a majority Muslim north and a mostly Christian south.
In recent years, its attacks have intensified in an apparent show of defiance amid the nation's military onslaught. Its ambitions appear to have expanded to the destruction of the Nigerian government.
How long has it been around?
The group was founded 12 years ago by Mohammed Yusuf, a charismatic cleric who called for a pure Islamic state in Nigeria. Police killed him in 2009 in an incident captured on video and posted to the Internet.
The crackdown, some say, made Boko Haram more violent and defiant.
Abubakar Shekau took control of the group and escalated the attacks. It murdered and kidnapped Westerners, and started a bombing campaign that targeted churches, mosques and government buildings.
Why not just kill Abubakar Shekau?
One word: elusive.
Questions have swirled about Shekau, including whether he's dead or alive. Even his age is unknown -- estimates range between 35 and 44.
In recent years, the Nigerian military has touted his death, only to retract its claim after he appeared alive and vibrant in propaganda videos.
He uses the alias Darul Tawheed, and analysts describe him as a ruthless loner and master of disguise. He does not speak directly with members, opting to communicate through a few select confidants.
Why would an Islamist militant group target the Muslim north?
Despite its religious fanaticism, Boko Haram does not consider all Muslims as supporters and allies.
There have been suggestions that it attacks certain mosques because members have spoken out against it and helped federal officials with their crackdown. Its attacks are aimed at striking fear at the heart of the local population to prevent cooperation with the government, analysts say.
Does the north support the group?
Although the northern populace mostly abhors the violence, there is considerable local sympathy and support for Sharia law, seen by many as the only way to end what is widely regarded as a corrupt and inept government. Poverty is prevalent in the northern region, and as the military struggles to halt Boko Haram's attacks, the militant group is winning perhaps its most important battle: making Nigerians question government competency.
Rights groups have accused local authorities of human rights violations in the fight against the group, adding to the anti-government sentiment.
What's the West doing to help?
The United States has put a $7 million bounty on Shekau's head. It also designated Boko Haram as a foreign terrorist network last year. Though it has provided technical and financial support to the Nigerian teams battling the insurgency, there has been a reluctance to put boots on the ground unless there's a direct national security threat to the West. Boko Haram's attacks have been limited primarily to Nigeria.
I don't live in Nigeria, so why should I care?
With a population of 175 million, Nigeria is Africa's most populous nation and is considered a political and economic powerhouse in the continent. The key U.S. partner is rich in oil, a major trading partner with China, and is the hub of global business in the region.
And as we've learned with Mali, any unresolved local Islamist insurgency has the potential of spiraling into a world problem.
Last year, Shekau released a statement vowing to attack the United States.
"Our strength and firepower is bigger than that of Nigeria. Nigeria is no longer a big deal to us, as far as we are concerned. We will now comfortably confront the United States of America," he said.
Does it have ties to al Qaeda?
The U.S. says Boko Haram has links to the al Qaeda affiliate in West Africa and to extremist groups in Mali.
What other attacks has the group conducted?
Just this week, a massive explosion ripped through a bus station in the Nigerian capital, killing at least 71 people. Though the group did not claim responsibility, the blast had the hallmarks of a Boko Haram attack.
In November, the group abducted dozens of Christian women, most of whom were later rescued by the military. Some were pregnant or had children, and others had been forcibly converted to Islam and married off to their kidnappers.
In 2011, a Boko Haram suicide attack on the United Nations building in Abuja killed at least 25 people.