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Former schoolteacher Chris Dawson is a "conniving monster" who betrayed his family, the brother of his murder victim Lynette has told a court.

A statement by Greg Simms was read out in the NSW Supreme Court, describing how the loss of his sister had impacted generations.

"We considered you an equal in all respects. We trusted you. You repaid us by committing the ultimate betrayal," Mr Simms wrote of Dawson.

Thursday's sentencing hearing comes 10 weeks after Dawson, now 74, was found guilty of murdering his wife in January 1982 to have an unfettered relationship with one of his high school students, known as JC.

"It was a brazen act of a conniving monster hell bent on one thing, getting what you wanted at any cost," Mr Simms said.

Wearing prison greens sitting in the court dock, Dawson listened to statements from Mr Simms as well as Lynette's sister Patricia Jenkins and his own daughter Shanelle Dawson who was four years old when her mother was killed.

Before reading her statement, Shanelle paused to stare at Dawson across the courtroom, breaking into tears before speaking.

"The night you removed our mother from our lives was the night you destroyed my sense of safety and belonging in this world," she said.

Her life had been shattered, she found it difficult to trust men, and she had been diagnosed with PTSD after learning what her father was capable of, she said.

"The torture of not knowing what happened, or what you did with her body - please tell us where she is. I hope you will finally admit the truth," she said.

Ms Jenkins said she had been "confused, alarmed, distressed and in a deep dark void" upon hearing of her sister's disappearance.

Dawson would lie to his daughters after the murder, telling them that Lynette wasn't their "real mother" but was only pretend because she had walked out, Ms Jenkins said.

"Lyn's disappearance and the journey has since taught me that no one is safe from tragedy. It can unexpectedly strike anywhere and justice can also be a long time coming."

Mrs Dawson went missing from the couple's Bayview home in Sydney's northern beaches when she was 33. Her body has never been found.

JC, who was also the family babysitter, was installed in the Bayview home as Dawson's partner days after he killed his wife.

Also on Thursday, crown prosecutor Craig Everson SC said Dawson had planned a "deliberate and conscious act" of domestic violence with an intention to kill.

He said a crime of "very great heinousness" required a term of life imprisonment.

In this case, Dawson's crime was heinous because of the significant harm to others, delays in the case and the ex-rugby player's lack of remorse, Mr Everson said.

Dawson's lawyer Greg Walsh disputed claims the crime was at the high end in terms of objective seriousness.

"This is not a case of such heinousness that it comes within the worst category of cases," he told the court.

He said Dawson had suffered under the "most constant and egregious publicity" for four decades.

His health was also deteriorating, with Dawson showing signs of chronic traumatic encephalopathy, a brain condition often experienced by those who play contact sports.

Dawson required extra protection while in custody, being threatened and taunted "day in, day out, minute after minute, hour after hour" by the name, The Teacher's Pet, Mr Walsh said.

The Teacher's Pet podcast by The Australian's Hedley Thomas shot the case into the public eye, garnering millions of views across the globe.

Dawson has already filed an appeal against his conviction.

Outside court, Mr Walsh told reporters that if this appeal failed, Dawson would die in jail.

Mr Simms, when asked whether he thought Dawson should perish behind bars, told reporters that his brother-in-law should do his time and again urged him to reveal where his sister's body was.

Justice Ian Harrison will deliver the sentence on December 2.

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Cyber Security Minister Clare O'Neil says the worst fears for Medibank customers have been realised, following the latest data dump of stolen customer information.

In a chilling message posted on the dark web, the ransomware group behind the hack released sensitive details of customers' medical procedures.

The group has also demanded $US1 for each of Medibank's 9.7 million customers.

Ms O'Neil told parliament she was appalled by the latest developments in the data breach.

"Yesterday, I indicated to the parliament that the consequences of the Medibank hack were likely to get worse, and today those fears have been realised," she said on Thursday.

"We stand with you. You are entitled to keep your health information private and what has occurred here is morally reprehensible and it is criminal."

Ms O'Neil said she had spoken with Medibank chief executive David Koczkar twice on Thursday to "make clear" community expectations.

She said she wanted to make sure affected customers would be able to access enough support.

"I don't want Australians to have to circulate 14 government departments or areas of Medibank in order to get what they deserve and need," she said.

"I received the assurance from Medibank today that if a large data dump occurs, they are fully ready to provide services when and if they are needed to Australians who need them."

The ransomware group began releasing Medibank data on the dark web in the early hours of Wednesday morning under files named "good-list" and "naughty-list".

The first wave included names, birthdates, addresses, email addresses, phone numbers, health claims information, Medicare numbers for Medibank's ahm customers and passport numbers for international student clients.

Mr Koczjar said the release of the data was disgraceful.

"The weaponisation of people's private information in an effort to extort payment is malicious, and it is an attack on the most vulnerable members of our community," he said in a statement.

"These are real people behind this data and the misuse of their data is deplorable and may discourage them from seeking medical care."

Australian Federal Police are ramping up efforts to catch those behind the huge data breach and are co-ordinating with state and territory police to support people at risk of identity fraud.

Operation Guardian, which was set up to tackle the recent Optus hack, is being expanded to investigate the Medibank data theft.

"If members of the community feel they are at imminent risk they should contact triple zero immediately," AFP Assistant Commissioner Cyber Command Justine Gough said.

Medibank has confirmed details of almost 500,000 health claims have been stolen, along with personal information, after the unnamed group hacked into its system weeks ago.

No credit card or banking details were accessed.

© AAP 2022

Former Olympic swimmer Scott Miller will spend at least three years in jail for playing the central role in a NSW drug ring.

The 47-year-old butterfly star was sentenced in the Downing Centre District Court to a jail term of five years and six months, with a non-parole period of three years - to be served from the date of his arrest in February 2021.

Miller has been in custody since pleading guilty to supplying a large commercial quantity of methamphetamine, supplying a commercial quantity of heroin, participating in a criminal group and dealing with the proceeds of crime.

Judge Penelope Hock said Miller's limited criminal history was consistent with someone who had a drug addiction.

"He was raised in a loving and supportive family environment, however at the age of 15 he was selected the attend the AIS in Canberra and it was there his mental health problems commenced," she said.

Miller won silver at the 1996 Atlanta Olympics, saying he was "devastated" at not winning gold.

Character references from Miller's swimming coaches and friends noted his struggles in adjusting after the Olympics.

"Miller's recurrent problems with depression and substance use date back to the sacrifices and pressures of his swimming career and the disappointment of not winning a gold medal when his purpose hinged on that one event," one reference said.

Miller was arrested on February 16, 2021 after an extensive police investigation pinned him at the centre of a criminal group.

Police tracked his movements over several days, monitoring him with tracking devices in his car.

In January 2021, he met up with an unidentified individual who placed a bag of candles containing $2 million worth of methamphetamine in his car.

Miller then hid the bag in a concealed compartment in his car before driving with his co-accused Wayne Allan Johnson to Yass.

In Yass the pair met up with two other co-accused, Justin Szabolics and Luke Peake at a motel.

There, the car was driven by Szabolics and Peake to Albury before the two dumped the candles and the car after a pursuit by police.

After finding the candles, police arrested and charged all four men.

Upon his arrest, police found heroin, cash and mobile phones in Miller's cupboard.

Judge Hock said the chances of rehabilitation for all the accused were good, and that they were at a crossroads in their lives.

"They are now in their mid to late 40s and they must recognise they are at a critical point, not only for them but for their families and friends who continue to love and support them," she said.

Miller will be eligible for parole in February 2024.

Szabolics was sentenced to three years in prison and will be eligible for parole in April 2024.

Johnson was sentenced to one year and 10 months' intensive correction order.

Peake's 15-month non-parole period ended in May after previously being sentenced to a maximum term of imprisonment of two years and six months.

© AAP 2022