A "phishing" email containing a virus sparked a cyber attack on two regional Victorian hospital networks.
Hospitals and health services in southwest Victoria and the Gippsland region were hacked on September 30.
"The cyber-attack began with a phishing email sent to an employee," a Victorian government statement confirmed on Friday.
"The email enabled a virus to download to the hospital's computer network, which provided cyber criminals with unauthorised access," it read.
No patient data was stolen but the government believes the aim of the attack was to extract payment rather than steal information.
Once the system was hacked the virus was spread across the network and led to the "ransomware" encryption of some servers.
"The actions taken by staff were effective at containing the spread of ransomware to just a portion of the hospital's computer network," it said.
The investigation involved a mix of state and federal police together with cyber security experts and private industry support.
Some hospitals had to cancel elective surgeries because of the security breach.
In the southwest region, Barwon Health chief executive Frances Diver told Melbourne radio in early October that 27 elective surgery cases had been cancelled.
The affected centres isolated and disconnected a number of systems to quarantine the infection.