Court Services Victoria was first made aware of the infiltration on December 21 and initially believed hackers accessed hearings from the Supreme, County, Magistrates and Coroners courts as far back as November 1.
It also warned an October recording from the Children's Court could have been compromised.
But Court Services Victoria on Thursday revealed some of the court files hacked were from before November 1, including some as old as 2016.
The cyber attack targeted Supreme Court matters heard in Ballarat in April 2016, along with others heard in Bendigo, Shepparton and Wodonga during parts of 2023, the statement said.
The hack also covered Supreme Court matters held in Melbourne's County building across six months in 2023.
Court officials previously thought the cyber attack only covered County matters dating back to November 1, but it in fact covered hearings there from April 4 to 6, 2016.
The hackers accessed more than four years' worth of County recordings dating from May 28, 2019 to January 1, 2023, CSV said.
"In many courts the system typically holds recordings for around 28 days, so the primary investigation period initially was 1 November to 21 December, which is when CSV identified the problem and isolated and disabled the affected network," CSV chief executive Louise Anderson said in a statement.
The updated date range for Coroners matters was from August 5, 2019 to December 21, 2023.
CSV discovered the hack was worse than previously thought after January 5, when it was able to analyse devices.
Staff would continue to alert people whose hearings at the Supreme, Magistrates, Children's and Coroner's courts had been hacked, but would focus on "particularly sensitive" County matters given the volume of affected cases, a statement said.
"Please be assured that CSV and the Courts continue to work on this process as a matter of priority," the CSV statement said.
"CSV is not currently aware of any unauthorised publication of the recordings.
"Monitoring of this will continue."
There was no change to the date range for the Magistrates Court, where targeted matters dated back to November 1.
The Children's Court and Victorian Civil and Administrative Tribunal were unaffected, CSV said.
The source of the hack has not been officially confirmed.
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