This study quantifies the effects of mergers on hospital data breaches, disrupting care, leading to fatal consequences, violating privacy rights, and incurring significant costs to remedy. Using U.S. hospital data over ten years, I provide causal evidence that data breach rates double during hospital mergers. The results suggest high pre-signing online visibility contributes to doubled data breach rates during mergers. Increased online visibility makes mergers more noticeable to malicious actors and increases external threats. Post-signing integration technical challenges is another factor for data breach risks. Effective management can mitigate the data breach risks in certain types of hospitals. By contrast, I find no evidence that the experience or resources of large multi-hospital health systems reduce the data breach risks. The study discusses the implications of predicting and managing data breach risks for hospital managers, health IT leaders, and healthcare authorities.