What you need to know about ISIS, which claims responsibility for the Brussels attack

A series of deadly bombings in Brussels killed at least 34 on Tuesday. Explosions rocked an international airport and a subway station. In a statement, ISIS claimed responsibility for the attacks.

“Islamic State fighters carried out a series of bombings with explosive belts and devices on Tuesday, targeting an airport and a central metro station in the center of the Belgian capital Brussels, a country participating in the coalition against the Islamic State,” the statement read.

“Islamic State fighters opened fire inside the Zaventem airport, before several of them detonated their explosive belts, as a martyrdom bomber detonated his explosive belt in the Maalbeek metro station.”

Since declaring its caliphate in June 2014, the self-proclaimed Islamic State has launched or inspired more than 70 terrorist attacks in 20 countries outside of Iraq and Syria. At least 1,200 people have died and more than 1,700 have been injured in those attacks.

Here’s what you should know about the terrorist group that New York magazine has described as “so vicious Al Qaeda wants nothing to do with them.”

How big is ISIS?

The group’s size is unclear, though a universal estimate suggests there are 10,000 ISIS fighters. The group claims to have thousands of foreign volunteers, some from Europe and the United States.

British media have reported that ISIS recruits non-Arab members with English-language videos and magazines.

U.S. intelligence officials have warned of ISIS attacks on U.S. soil in the coming year.

In February, top U.S. intelligence officials said ISIS would continue attacks in Europe and was likely to try a direct attack on the United States in 2016.

Officials reported that about five dozen people linked to the terrorist group were arrested in the United States in 2015.

At a Senate Armed Services Committee hearing, Director of National Intelligence James Clapper estimated that violent extremists were active in about 40 countries and there are more terrorist havens “than at any time in history.”

He said that ISIS terrorists are hiding among refugees fleeing Iraq and Syria to gain entry into other countries. Clapper said they were “pretty skilled at phony passports so they can travel ostensibly as legitimate travelers.”

How the world is fighting ISIS

Never heard of Operation Inherent Resolve? Then you’re not following the world’s fight against ISIS on Twitter.

You probably haven’t checked out the military operation’s website, either. (Click here.)

Since August 2014, the U.S. military and an international coalition of nations have conducted nearly 11,000 targeted air strikes against ISIS in Iraq and Syria, according to Department of Defense statistics.

The United States has conducted the majority of those strikes — about 8,300 — at a cost of $6.5 billion, according to government stats.

At least a dozen nations have participated in the strikes, including Australia, Belgium, Canada, Denmark, Jordan, the United Kingdom, Saudi Arabia, the United Arab Emirates and France.

After the Paris attacks in November the French conducted several waves of airstrikes against ISIS targets in Syria. Raids by the U.S.-led coalition and Russia killed dozens of militants.

According to Air Force statistics, the United States dropped 2,694 bombs in January and 2,054 in February in Iraq and Syria, down from the height of the air war in November and December.

The lull in the airstrikes comes as the United States prepares to send the B-52 Stratofortress to the Middle East to supplement airstrikes. It is expected to arrive in April.

Anonymous hackers are “at war,” too

Turning Twitter into a cyberspace battleground, the hacking collective Anonymous declared “war” on ISIS after the Paris attacks and launched its “biggest operation ever.”

Anonymous claimed to have shut down more than 5,000 Twitter accounts and websites belonging to the extremists. The group also begun leaking personal information about suspected terrorists and ISIS recruiters.

Tech-savvy ISIS uses the Internet and mainstream platforms including Twitter, Facebook and YouTube to distribute information and market the group’s work. Members know how to write code and hack, too.

After the attacks in Paris, ISIS sent out a call to its followers on the messaging app Telegram — apparently popular with the terrorists — “to unite (their) profile pictures on Twitter” with an image of a black shoe print on the French flag.

Who leads ISIS?

Several of the group’s top leaders have been killed, including the No. 2 man in charge, Haji Mutazz, who died in a drone strike near Mosul, Iraq, in August.

The group’s current leader is a 40-something Iraqi named Abu Bakr al-Baghdadi, who assumed control in May 2010. He was rumored to have been killed in a March airstrike by the U.S.-led coalition, but those reports appear unfounded.

His nickname is “the invisible sheik” because he wears a mask when he addresses his commanders.

A report by British media in February claimed that al-Baghdadi’s wife, a German teenager named Diane Kruger, had fled Iraq with two other women. Her husband reportedly sent troops to drag her back.

Kruger reportedly headed up a special military camp in Kirkuk where women are trained to carry out suicide bombings.

What happened to the Paris bombers?

Abdelhamid Abaaoud, the Belgian jihadi suspected of masterminding the Paris attacks, was later killed in a police raid on a suburban apartment building.

Senior ISIS leader Omar al-Shishani, the group’s minister of war, recently died of wounds sustained in a March 4 airstrike by the United States near the Syrian city of Shaddadi.

Last week, Salah Abdeslam, a suspect in the Paris attacks and deemed Europe’s most wanted fugitive, was arrested during a raid on an apartment in Brussels. Belgium officials said the suspected terrorist was “worth his weight in gold.” He is the only surviving participant in the attacks in police custody.

Abdeslam’s lawyer told media that his client was “not maintaining his right to remain silent.”

What does ISIS want?

One goal is to create a new radical Islamist state, combining parts of Syria and Iraq.

Today it controls hundreds of square miles, “a nation-sized tract of territory,” according to The Washington Post, all the way from Syria’s Mediterranean coast to south of Baghdad.

ISIS runs its own version of “government” in the towns it has seized, running its own courts, schools and services.

Odd note: CNN reported that in Raqqa, ISIS launched its own consumer protection agency to monitor food standards.

The group’s black-and-white flag flies over much of what it it controls.

What else does it want?

Some believe ISIS wants to create chaos.

Harleen Gambhir, an analyst at the Institute for the Study of War, tells The New York Times that not only does ISIS want to build relationships with jihadists who can carry out military operations across the Middle East and Africa, it wants to inspire its sympathizers to attack the West.

“The goal is that through these regional affiliates and through efforts to create chaos in the wider world, the organization will be able to expand, and perhaps incite a global apocalyptic war,” Gambhir said.

A timeline of ISIS terror in 2015 and early 2016

Jan. 10 – An online video shows Taliban fighters in Pakistan pledge loyalty to the Islamic State group and behead a man they identify as a soldier. Similar pledges previously arose from Egypt, Yemen and elsewhere in the Mideast. Afghan authorities later acknowledge a similar presence in their country.

Jan. 24 – A message claims the Islamic State group beheads Japanese hostage Haruna Yukawa, a 42-year-old adventurer, after earlier demanding $200 million for him and captive Japanese journalist Kenji Goto. Japanese and Jordanian officials attempt to negotiate a prisoner swap to free him and captured Jordanian pilot 1st Lt. Mu'ath al-Kaseasbeh.

Jan. 31 – The Islamic State group releases a video saying it beheaded Goto.

Feb. 3 – The Islamic State group releases a video of it burning al-Kaseasbeh to death in a cage, sparking outrage in Jordan, which launches new strikes targeting the militants.

Feb. 15 – Libyan militants who earlier pledged their loyalty to the Islamic State group behead a group of Coptic Christians from Egypt in an online video.

Feb. 16 – Egypt launches airstrikes in Libya in retaliation for the beheadings.

March 20 – A group identifying itself as an affiliate of the Islamic State group in Yemen claims a series of suicide bombings killing 137 people and wounding 345, though U.S. officials express skepticism about the claim.

April 18 – Afghan President Ashraf Ghani blames the Islamic State group for a suicide bombing in the country that kills at least 35 people and wounds 125.

April 19 – Islamic State affiliates in Libya release a video showing them behead and shoot dead groups of Ethiopian Christians, slayings resembling the February beheadings of the Egyptian Coptic Christians.

Aug. 5 – An affiliate of the Islamic State group threatens to kill Croatian hostage Tomislav Salopek in 48 hours unless Egypt releases “Muslim women” it holds in prison.

Aug. 12 – An online image purports to show Salopek beheaded by the Islamic State affiliate in Egypt.

Aug. 13 - ISIS claims responsibility for a truck bombing at a Baghdad produce market that kills at least 62 people and wounds more than 200.

Aug. 19 - ISIS beheads Khaled al-Asaad, retired chief of antiquities for Palmyra, who helped hide away treasures for safekeeping from the terrorists.

Sept. 2 - ISIS supporters in Yemen claim responsibility for two bombings at a mosque that kill at least 20 people.

Sept. 17 - ISIS claims responsibility for a car bomb in an Iraqi town that kills 90, including children, and leaves more than 100 wounded at the end of the Muslim fasting month of Ramadan.

Sept. 24 - ISIS followers in Yemen claim responsibility for a suicide bombing at a mosque in the Yemeni capital Sanaa that kills at least 29 people attending Eid prayers.

Sept. 29 - ISIS claims responsibility for the shooting death of an Italian aid worker in Bangladesh.

Oct. 3 - ISIS claims responsibility for the shooting and killing of a Japanese man in Bangladesh, the second murder of a foreigner by ISIS in the country within a week.

Oct. 10 - Turkish authorities blame ISIS for two explosions in the heart of the capital, Ankara, that kill at least 95 people and wound more than 200 at a peace rally. They are called the deadliest terrorist attacks in modern Turkey history.

Oct. 24 - Three bombs explode in Bangladesh during a large procession commemorating the Shiite Muslim holiday of Ashura. One person dies, dozens are wounded. ISIS claims responsibility.

Oct. 31 - ISIS claims responsibility for the downing of a Russian airliner carrying 224 people. No one survives. ISIS calls it retaliation for Russian air strikes against it.

Nov. 4 - ISIS claims responsibility for a suicide bombing next a police club in northern Sinai that kills four police officers and leaves at least five civilians wounded.

Nov. 12 - ISIS claims responsibility for a double suicide bombing in southern Beirut that kills at least 43 people and wounds more than 200.

Nov. 13 - ISIS claims responsibility for attacks in Paris attacks that kill 129 and leave 352 injured, including at least 99 seriously.

Dec. 2 - Tashfeen Malik and her husband, Syed Rizwan Farook, shoot and kill 14 people and injure 21 others in San Bernardino, Calif. The two are later gunned down in a shootout with law enforcement. Malik had pledged allegiance to ISIS leader Abu Bakr al-Baghdadi on Facebook.

Dec. 15 - In an attack believed to have been inspired by ISIS, a 29-year-old man cuts another man’s throat in the Leytonstone Underground station in London. The attacker reportedly shouted, “This is for Syria, my Muslim brothers.” British media reported that this cell phone contained images and flags associated with ISIS.

Jan. 7, 2016 – Police in Paris shoot and kill a man wielding a large knife outside a metro station. Prosecutors later say he had a sketch of an ISIS flag and had pledged allegiance to al-Baghdadi.

March 19 - U.S. Marine Marine Staff Sgt. Louis Cardin of Temecula, Calif., dies in an ISIS rocket attack at a base in northern Iraq. It was the second combat death of an American service member in Iraq since the campaign to fight ISIS began.

March 22 - Bombs exploded at the Brussels airport and one of the city’s metro stations Tuesday, killing scores of people and wounding dozens more. ISIS says its extremists opened fire and detonated suicide belts in the airport.

This story was originally published March 22, 2016 at 2:11 PM with the headline "What you need to know about ISIS, which claims responsibility for the Brussels attack."