A data breach at Connecticut’s largest healthcare system Yale New Haven Health affects more than 5.5 million people, according to a legally required notice with the U.S. government’s health department.

Yale New Haven said the March cyberattack allowed malicious hackers to obtain copies of patients’ personally identifiable information and some healthcare-related data. 

Per a notice on the healthcare system’s website, the stolen data varies by person, but can include patient names, dates of birth, postal and email addresses, phone number, race and ethnicity data, and Social Security numbers. The stolen data also includes information about types of patients and medical record numbers.

Local media quoted the healthcare system’s spokesperson as saying that the number of affected individuals “may change.” A spokesperson for Yale New Haven did not immediately comment when contacted by TechCrunch.

This is the second major healthcare data breach confirmed this week, after Blue Shield of California revealed it shared health data of 4.7 million patients with Google over several years.