Vice-chancellor Brian Schmidt said the university was working with government security agencies to investigate the breach,which occurred in late 2018 and was detected two weeks ago.
"We believe there was unauthorised access to significant amounts of personal staff,student and visitor data extending back 19 years,"Professor Schmidt said in a letter to students and staff.
"Depending on the information you have provided to the university,this may include names,addresses,dates of birth,phone numbers,personal email addresses and emergency contact details,tax file numbers,payroll information,bank account details,and passport details. Student academic records were also accessed."
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Professor Schmidt said there was"no evidence"research work had been affected.
A university spokesman estimated the number of people affected was 200,000,based on annual student numbers and staff turnover.
Authorities said it was too early to say who was behind the attack,nor whether it was linked to a separate breach of the university's systems more than a year ago,which national security sources said was the work of the Chinese government.