A massive cybersecurity incident has exposed the personal health records of an estimated 15 million patients across multiple hospital systems in North America. The breach, discovered last week, is being called one of the largest healthcare data compromises in history.

The attack exploited a vulnerability in widely-used healthcare management software, allowing unauthorized access to patient names, medical histories, insurance information, and in some cases, Social Security numbers.

Federal investigators are working alongside cybersecurity firms to determine the full scope of the breach. Affected hospital systems have begun notifying patients and are offering free credit monitoring services.

The incident has reignited calls for stronger cybersecurity regulations in the healthcare sector, where aging IT infrastructure often leaves systems vulnerable to sophisticated attacks.