<p>Product market competition creates a strategic trade-off where managers withhold information to minimize proprietary costs or disclose it to signal strength. This study investigates how this classic relationship unfolds within a unique institutional environment. We focus on earnings conference calls in China, where the true identities of the questioners are anonymous to managers. Using import tariff reductions as an exogenous shock to competition, we find that intensified product market competition leads to a significant reduction in disclosure. Managerial responses become shorter, contain less quantitative information, and are less comprehensible. To provide evidence that this reduction is driven by the anonymity of questioners rather than a general competition effect, we exploit variations in the intensity of anonymity. The results show that the defensive silence is significantly stronger when high question volumes amplify the competitive espionage threat, and when low analyst attention exacerbates signaling and screening difficulties. Further analysis using topic modeling shows that managers selectively reduce discussions on competitive advantage to limit information leakage and reduce discussions on profit distribution due to signaling frictions. They also limit discussions on investment and financing, a topic subject to both pressures. Our findings demonstrate that anonymity in the communication channel acts as an important environmental constraint, leading managers to prioritize information security over communication efficiency when facing competition.</p>