In a recent literary analysis of George Orwell's '1984', the term insidious is often used to critique the subtler mechanisms of totalitarian control. The author argues that while overt oppression is alarming, it is the insidious propagandistic tactics employed by the regime that sow seeds of fear and compliance among the populace, leading them to accept their own subjugation.

Which of the following best captures the meaning of insidious as used in this context?