Information plays a key role in natural disaster crisis management and relief. A new generation of lightweight UAVs may help improve the situational awareness and assessment. They may first of all relieve rescue teams from time-consuming data collection tasks. At the same time, those UAVs may assist research operations through a more insightful and automated guidance thanks to advanced sensing capabilities. In order to achieve this vision, two challenges must be addressed though. The first one is to achieve a sufficient autonomy for such vehicles, both in terms of navigation and of interpretation of the data sensed. The second one relates to the reliability of the UAV with respect to accidental (safety) or malicious (security) risks. This paper first discusses the potential of UAV assistance in several humanitarian scenarios, as well as potential problems in such situations. The question of autonomy is then addressed. Finally, a secure embedded UAV architecture that relies on cryptographic protocols and on specific hardware capabilities is sketched.