The antonym for "most shielded" can be "most exposed". When something or someone is "most exposed", they are vulnerable to harm or danger. If a person is in the open with no protection, they are exposed to the elements, which can be harmful to their health. Similarly, a secret that is not guarded is exposed to anyone who wishes to exploit it. A vulnerable person or thing is easy prey for predators, and their safety is at risk. In contrast, when an object or person is shielded, they are protected from harm or danger. Therefore, it is important to shield or protect sensitive information and vulnerable individuals to prevent them from being exposed to hazards.