A recent data breach incident has been reported at Yale New Haven Health, Connecticut’s largest healthcare system, affecting over 5.5 million individuals, as disclosed in a mandatory notice filed with the US Department of Health and Human Services, which can be accessed here.

According to Yale New Haven Health, a cyberattack occurred in March, resulting in malicious hackers obtaining unauthorized access to patients’ personal identifiable information and certain healthcare-related data.

As stated on the healthcare system’s website, in a public notice, the compromised data varies among individuals but may include patient names, birth dates, postal and email addresses, phone numbers, racial and ethnic data, and Social Security numbers. Additionally, information about patient types and medical record numbers was also stolen.

Local news outlets have quoted a spokesperson for the healthcare system, who mentioned that the number of affected individuals may be subject to change.

When questioned by TechCrunch about the nature of the cyberattack, Yale New Haven spokesperson Dana Marnane did not deny that the incident was related to ransomware attacks.

Marnane stated, “The sophistication of the attack suggests that it was carried out by an individual or group with a history of similar incidents,” but declined to provide further comment due to an ongoing law enforcement investigation.

The healthcare provider has chosen not to disclose whether it has had any communication with the hackers or if a ransom demand was made.

As of the latest update, no prominent ransomware group has publicly claimed responsibility for the hack. However, it is common for ransomware and data extortion groups to publish stolen files if ransom negotiations fail.

This incident marks the second significant healthcare data breach reported this week, following the revelation by Blue Shield of California that it shared the health data of 4.7 million patients with Google over several years.

This article has been updated to include additional comments and details related to ransomware attacks.