Those affected will receive a letter between now and April 2023 informing them.
The HSE’s Chief Information Officer Fran Thompson says Gardaí managed to secure the data targeted by the hackers and return it to the HSE.
The HSE then worked to verify the information and identify those impacted.
84% of the data was that of patients, while 16% of it related to staff.
The information is a mix of personal, medical, employee and limited financial information.