There are a couple of potential concerns of national security which explain Malaysian officials being cagey about the radar "blip" which (presumably) turned out

There are a couple of potential concerns of national security which explain Malaysian officials being cagey about the radar "blip" which (presumably) turned out to be MH370: 1. The exact locations and ranges of military radar capabilities is considered secret, if other countries knew their exact locations/abilities it would make an attack easier. This would make them reluctant to say where they picked it up/lost it on radar as it could reveal the range of the radar. 2. If the radar blip wasn't MH370, what was it? It could have been a drone from any number of countries, or a spy plane flying over, or any number of potentially embarrassing possibilities that a military commander would have trouble admitting had gone mostly unnoticed for 72 hours.