In an unstable world, sophisticated weapons once only wielded by nation-states are increasingly falling into the hands of extremists, rebels, and other non-state actors. Just this week, Hamas has fired long-range missiles from Gaza into Israel cities, well-armed Islamic extremists in northern Iraq are pushing back the army, and a Malaysia Airlines passenger jet was shot down over Ukraine. In fact, commercial airliners—long targeted by militants—may be the most vulnerable marks out there. As these arms proliferate, it’s fortunate that more of them haven’t been shot down. 

U.S. intelligence officials have confirmed that the Malaysian flight was bought down in an area of Eastern Ukraine controlled by pro-Russian separatists, quite possibly by a long-range, BUK surface-to-air missile battery. These self-propelled air defense platforms boast their own radars and have an operational range of roughly 72,000 feet. Journalists recently reported seeing a BUK battery in the rebel-controlled region of the crash. 

Because the Malaysian airliner was flying at roughly 33,000 feet and in excess of 600 miles-an-hour, the Boeing 777 was well out of the range of the shoulder-fired, man-portable air defense systems that the Ukrainian rebels also wield. But Ukrainian officials have confirmed that one of their military jets was hit by a rebel-fired MANPAD, though the pilot was able to land the damaged plane. In two earlier attacks in the recent months, rebels downed two military helicopters with missiles, killing 23 soldiers including a Ukrainian general. 

Stinger man-portable missiles may also threaten the U.S. Army crews of Apache helicopter gunships recently dispatched to Baghdad to secure the airport and defend the U.S. embassy. Intelligence reports say that the Islamic State organization, also known as ISIS, has likely captured U.S.-made Stingers. In seizing major cities such as Mosul and Tikrit, and overrunning four Iraqi army divisions, Islamic State fighters have reportedly taken control of two major weapons depots, where Stingers were likely stored along with other sophisticated U.S.-manufactured armaments. 

American officials know how much havoc their missiles can wreak in the wrong hands. After the fall of Moammar Gaddafi in Libya in 2011, his arsenals were looted of as many as 15,000 portable surface-to-air missiles, most of them Russian-made SA-7s. U.S. officials found the prospect so alarming that they mounted a $40 million “buy back” program for the missing Libyan MANPADS, much as the CIA had purchased back Stingers given to the Afghan mujahedeen in their fight against the Soviets during the 1980s. The Stingers ultimately destroyed more than 250 Soviet military aircraft in Afghanistan and turned the tide of the war, but as recently as 2005, the CIA was still trying to buy back Stingers missing from the conflict. 

Despite the U.S. buy-back program, Gaddafi’s SA-7 MANPADS were later discovered by both Algerian and Egyptian authorities. In January, Islamist militants in the Sinai Peninsula shot down an Egyptian military helicopter with one of the missiles, killing five soldiers. Hamas also claims that it also possesses MANPADS. 

The threat that these missiles pose to civil aviation is not hypothetical. In 2002, al-Qaeda-linked terrorists in Mombasa, Kenya targeted an Israeli charter flight with 261 people onboard, narrowly missing the aircraft with SA-7 missiles. That attack and the proliferation of the weapons prompted the Israelis to develop the “SkyShield” defense system for commercial airliners. It protects aircraft against shoulder-launched missiles, especially during takeoffs and landings, when the aircraft are vulnerable to short-range missiles. Earlier this year, Israeli officials said SkyShield was finally ready to deploy. 

A report by the Arms Control Association estimates that 47 non-state groups worldwide now possess MANPADS, which have already been used in 50 attacks against civilian aircraft that have killed nearly 1,000 civilians. In 1994, a MANPADS attack downed an aircraft carrying the leaders of Rwanda and Burundi, sparking a genocide that killed more than 800,000 Rwandans. A 2005 report by the RAND Corporation estimated that the direct costs of a single successful missile attack on a commercial airliner could approach $1 billion, and ultimately climb higher to as much as $16 billion if it depressed demand among the flying public for an extended period. 

“The proliferation of MANPADS has been a major concern for a long time, but as the custody of large stockpiles of these weapons comes into question the threat to civil aviation definitely increases,” said Daryl Kimball, executive director of the Arms Control Association. “The Malaysian airliner suggests that along with the MANPADS threat we now have seen a much more sophisticated surface-to-air missile used to attack a civilian airliner, and that system is in the arsenal of both Russia and Ukraine,” he added. The one that hit the cruising-altitude Malaysia flight was a military grade weapon, but shoulder-mounted versions now controlled by militants around the world mean that any low-flying jet in the wrong airspace could add to the death toll.