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Yale New Haven Health (YNHHS) has confirmed a significant data breach impacting 5.5 million patients. The cybersecurity incident, which occurred in March, involved unauthorized access to YNHHS systems, leading to the potential theft of sensitive personal information. The exposed data includes names, dates of birth, medical record numbers, and in some instances, Social Security numbers and health insurance details. YNHHS has alerted affected patients and is working with law enforcement and cybersecurity experts to investigate the breach.

Mandiant's incident response team was brought in to help contain the breach. The healthcare system began notifying affected patients via mail on April 14. The organization is affiliated with Yale University and Yale School of Medicine and is Connecticut's largest provider of its kind, with five hospitals and medical clinics throughout the US state as well as New York and Rhode Island.

This cyberattack is considered one of the largest healthcare data breaches of the year. YNHHS has stated that the incident has not affected its ability to provide patient care, with the patient portal and electronic medical records functioning normally. The incident serves as a stark reminder of the increasing cyber threats faced by healthcare organizations and underscores the critical need for robust security measures to safeguard patient data.

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References :

• The Register - Security: SSNs and more on 5.5M+ patients feared stolen from Yale Health
• Security Affairs: Yale New Haven Health (YNHHS) data breach impacted 5.5 million patients
• The DefendOps Diaries: TheDefendOpsDiaries: The Yale New Haven Health Data Breach: A Wake-Up Call for Healthcare Cybersecurity
• BleepingComputer: Yale New Haven Health data breach affects 5.5 million patients
• cyberinsider.com: Yale New Haven Health has officially confirmed that a March cybersecurity breach impacted over 5.5 million individuals, making it one of the largest healthcare data incidents reported in 2025.
• www.itpro.com: More than 5 million Americans just had their personal information exposed in the Yale New Haven Health data breach – and lawsuits are already rolling in
• Tech Monitor: Yale New Haven Health data breach exposes data of 5.5 million patients
• Zack Whittaker: New: Connecticut's largest healthcare system, Yale New Haven Health, says a data breach affects at least 5.5 million people. When I asked about the nature of the incident, a spokesperson said the hack tracks as ransomware and that law enforcement are investigating.
• techcrunch.com: Data breach at Connecticut’s Yale New Haven Health affects over 5 million
• techcrunch.com: Data breach at Connecticut’s Yale New Haven Health affects over 5 million
• Talkback Resources: Yale New Haven Health alerts 5.5M+ patients of data breach
• CyberInsider: CyberInsider: Yale New Haven Health Confirms 5.5 Million Affected
• www.scworld.com: Over 5.5M impacted by Yale New Haven Health breach
• lifehacker.com: This Healthcare Data Breach Compromised 5.5 Million Patients' Information
• CyberInsider: CyberInsider: VeriSource Breach Exposes Personal Data of 4 Million Individuals

Classification:

• HashTags: #DataBreach #CyberAttack #HealthData
• Company: Yale New Haven Health
• Target: Yale New Haven Health Patients
• Product: YNHHS Systems
• Feature: Data Theft
• Type: DataBreach
• Severity: Disaster