[spartango]

When you say that national intelligence communities are secretive, you're absolutely right. So much so that they would certainly not share any sort of information with commercial/multinational airlines. It sounds ridiculous, given that lives are at stake, but it is important to consider their calculus (taking the US intel perspective for a moment):

Knowledge that rebels had active radar-guided SAMs would be derived from a handful of classified assets, from satellite to radar to drone to people. Adversaries to the US are meant to be unaware of these modalities (to prevent countermeasures), but you can bet they are all in use.

The challenge is that disclosure of any facts gleaned from classified systems potentially reveals their capabilities.

Now disclosure is a continuous spectrum, from "there is a threat" to "here is a multispectral image of a launcher", so perhaps there is some shareable information. In considering that, you weigh the utility (external risk) of the information shared against its credibility (details), and the potential loss of capability incurred by disclosure. When we say "loss of capability", in this case it may mean disclosing the capability to detect missile launches early, which represents a critical piece of US missile defense.

For a historical case study in this type of calculus, it's worth looking into the disclosure of images during the Cuban Missile crisis. There, the US had to provide credible information that there was a threat in Cuba, and did so at the cost of the revelation of U-2 images.

By the way, this same calculus played into the US President's wording when he spoke yesterday about the tragedy. Obama was careful to say little about how they knew where the missile came from.

Unfortunately, from the perspective of an intelligence agency, NDAs are insufficient to protect classified assets, especially where multinationals are involved. Anything that is disclosed would go through several levels of indirection, and would probably end up in a NOTAM (like the one prohibiting flight under FL320 in the region).