"Power of Words": Stealthy and Adaptive Private Information Elicitation via LLM Communication Strategies

While communication strategies of Large Language Models (LLMs) are crucial for human-LLM interactions, they can also be weaponized to elicit private information, yet such stealthy attacks remain under-explored. This paper introduces the first adaptive attack framework for stealthy and targeted private information elicitation via communication strategies. Our framework operates in a dynamic closed-loop: it first performs real-time psychological profiling of the users' state, then adaptively selects an optimized communication strategy, and finally maintains stealthiness through prompt-based rewriting. We validated this framework through a user study (N=84), demonstrating its generalizability across 3 distinct LLMs and 3 scenarios. The targeted attacks achieved a 205.4% increase in eliciting specific targeted information compared to stealthy interactions without strategies. Even stealthy interactions without specific strategies successfully elicited private information in 54.8% cases. Notably, users not only failed to detect the manipulation but paradoxically rated the attacking chatbot as more empathetic and trustworthy. Finally, we advocate for mitigations, encouraging developers to integrate adaptive, just-in-time alerts, users to build literacy against specific manipulative tactics, and regulators to define clear ethical boundaries distinguishing benign persuasion from coercion.