Aviation Week shows a photograph of a big piece of aircraft skin, well peppered with shrapnel holes, taken at the Ukrainian crash site. Clear evidence of the detonation of a warhead close aboard. The wreckage bears Malaysia Airlines red and blue stripe paint scheme.
Malaysia Air was not alone in the Ukrainian skies. Air India flt 113 and Singapore Airlines Flt 351 were on the same air routes and only a few miles away when Flt 17 was struck by the SAM. Malaysia Air was not the only target in the air that day, it was merely the unlucky one that got hit.
There does not appear to be any international organization to designate dangerous airspace and warn airman away from it. The closest approach to such an organization is the US FAA, which has designated pest holes like North Korea as no fly zones. FAA has a good reputation for competence and non partisan ship and so most airlines around the world follow FAA recommendations, even though the foreign airlines are not bound to do so by law.
The SAM used for the shootdown bears the NATO designation of SA-11 Gadfly. It's Russian makers call it BUK-M1, but the NATO designation is more widely known. Each SA-11 launcher vehicle carries 4 to 6 missiles and the radar to aim them and can launch independently of central control. The launchers do NOT carry Identification Friend or Foe (IFF) equipment, a WWII technology still in use today. IFF equipped aircraft return a coded message to ground radars. All airliners on international routes carry IFF. SA-11 launch vehicles are designed to plug into a central command trailer with the NATO designation of Snow Drift. The Snow Drift does have IFF equipment. It is likely that the SA-11 launcher that hit the airliner was not plugged into a Snow Drift and thus did not have any IFF information available to its crew.