A ransomware group has begun posting client data stolen from Australia’s largest health insurer on the dark web.

Hundreds of names, addresses, birthdates and Medicare details were being posted under “good-list” and “naughty-list” on a blog belonging to the group.

The hackers had demanded a ransom to stop them from releasing the data, but Medibank earlier this week said it would not pay it because it would encourage further crime.

Shortly after midnight, the group posted the first lists.

“Looking back that data is stored not very understandable format (table dumps) we’ll take some time to sort it out,” they said in the early hours of Wednesday.

“We’ll continue posting data partially, need some time to do it pretty.”

The hackers also appeared to have revealed screenshots of private messages recently exchanged between themselves and Medibank representatives.

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Medibank has previously confirmed almost 500,000 health claims were stolen, along with personal information, when the unnamed group hacked into its system weeks ago.

Some 9.7 million current and former customers have been affected.

No credit card or banking details were accessed.

Assistant treasurer Stephen Jones blasted the hackers on Wednesday.

“They’re scumbags, they’re crooks, they’re criminals and we shouldn’t be paying ransom,” he told Sky News.

“We shouldn’t be giving in to these fraudsters. The moment we fold it sends a green light to scumbags like them throughout the world that Australia is a soft target. We cannot give in and we won’t give in.”

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Mr Jones said Australia needed to quickly lift protection against cyber threats.

On Tuesday, the ransomware group posted to its blog that “data will be publish (sic) in 24 hours”.

“P.S. I recommend to sell (sic) medibank stocks.”

Medibank apologised again to clients past and present on Tuesday. It advised customers to be alert for any phishing scams via phone, post or email.

“We knew the publication of data online by the criminal could be a possibility but the criminal’s threat is still a distressing development for our customers,” CEO David Koczkar said on Tuesday.

Medibank is certainly not alone in refusing to pay a ransom demand, with a recent report finding 19 per cent of Australian companies responded to ransomware attacks by paying the fee.

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Mimecast’s 2022 State of Ransomware Readiness report found 20 per cent of companies were asked to pay between $500,000 and $999,999 for their information

Some 13 per cent of the businesses surveyed said the total cost of the ransomware attacks they’d experienced was between $1 million and $2 million.

© AAP 2022

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