security risk
person who, because of his political beliefs, personal habits, etc may endanger the security of the state, eg by revealing secrets to an enemy (威胁国家安全的)危险人物
She's a poor/good security risk. 她是个不太[十分]危险的人.
And so with solids such as a shell, a nut, a plum, a pear, a tadpole, a mushroom, a mountain peak, a kidney, a carrot, a tree-trunk, a bird, a bud, a lark, a ladybird, a bulrush, a bone.