Military experts think that a Buk missile — an easy-to-use type of anti-aircraft weapon — is the most likely culprit in the destruction of a Malaysian Airlines passenger jet that's thought to have been shot down over eastern Ukraine.

These missile launchers are specially created for hitting high-altitude aircraft, and can fire at targets of up to 80,000 feet.

But unless linked to other weapons or an air traffic control system, they are almost incapable of telling the difference between military and civilian aircraft. The Buk is mobile, easy to use, and capable of hitting aircraft at all but the most outlandish altitudes. Yet as the MH17 disaster proves, that comes with a huge potential drawback, especially when the weapon is in the hands of people incapable of using it responsibly.

Pro-Russian separatists have apparently admitted that they have Buk missiles. These weapons reach far higher altitudes than the shoulder-fired rocket launchers that pro-Russian separatists have been using to destroy Ukrainian aircraft during the past week, high enough that they could reach the over 30,000-feet altitude at which the airliner was flying.

The missiles are straightforward to operate and work as stand-alone weapons — they can function outside of a sophisticated networked air defense system.

While that's useful in some respects it also makes it unnervingly easy to make a mistake, particularly for guerrilla or non-conventional fighters who are capable of firing the easy-to-use missiles, but don't have the training needed to distinguish between civilian and military aircraft by sight.

As one expert explained to Technology Review, the Buk's ease of usability is also what makes the weapon so prone to tragic and costly errors like the MH17 crash.

The system cannot tell the difference between civilian and military-type aircraft based on their transponder signatures alone. In order to tell the difference between targets, it would need to be interfaced with other weapons systems that can work off of additional information.

Being a Soviet design, the user interface is fairly simple, says Michael Pietrucha, a former F-4G and F-15E electronic warfare officer and expert on air defenses. Pietrucha says he trained with German forces operating a similar Russian-built system during the 1990s.

Pietrucha says that the Buk variant operated by the rebels might have been especially unable to distinguish between civilian and military air traffic because of a quirk related to aircraft transponders. The transponder is a device that broadcasts an aircraft’s identity when a radar "interrogates" it for information.

Military and civilian aircraft often use the same transponder modes and therefore that signal is not used as a "discriminator" for a military targeting system, Pietrucha says. The system has to be tied into the national air traffic control system to use that information effectively.

So the Buk can pick up the signal of an aircraft. But if it's operating in standalone mode, it can't tell whether that aircraft is a military target, or a jetliner with nearly 300 people onboard.

As Thomas Gibbons-Neff reported in the Washington Post, the Buk can be interfaced with other systems, but U.S. intelligence sources believe the Buk was the only one anti-aircraft system operating in the area of the crash at the time the plane was shot down.

The transponder explanation seems likeliest here: Whatever unit shot down MH17 simply couldn't see if it was a civilian or military aircraft — they could just see it was an aircraft in their airspace — because it wasn't hooked up to a system that would have made such recognition possible.

On some models of the weapon, radar systems are rudimentary at best. With untrained irregular soldiers at the helm, even a linked system could have made a terrible mistake. To the right is a GIF of a Buk M2 surface-to-air system in action. The radar and firing interface are relatively simple and user-friendly.

"This definitely could have been an error," Steve Zaloga, an expert on missile systems at the Teal Group, told Technology Review.