“This claims data includes the location of where a customer received medical services, and codes relating to their diagnosis and procedures.”

The insurer announced a trading halt as details of the hack emerged on Wednesday morning.

The hackers threatened to leak or sell the data, starting with 1,000 high-profile Australians, unless Medibank paid a ransom.

The company did not say how many of its 4 million customers were likely to have been affected but warned the number was likely to rise. The Australian Federal Police said they had opened an investigation into the breach, without commenting further.

The Optus hack was one of largest data breaches in Australian history.

Home Affairs Minister Clare O’Neil said on Thursday that cybersecurity could no longer be taken for granted.

“Combined with Optus, this is a huge wake-up call for the country,” she told ABC Radio.

“This is the new world that we live in. We are going to be under relentless cyberattack, essentially from here on in.”

Cybersecurity experts said it was unclear whether the data breach disclosures were related, given the varied nature of the attacks, but the publicity generated by the Optus attack may have drawn attention in hacker networks.

“When you do have a highly visible breach like Optus in Australia out there, hackers take notice of that and go ‘maybe I’ll have a go down there and see what I can get away with,’” said Jeremy Kirk, executive editor at Information Security Media Group, a cybersecurity specialist publication.

Larger Optus rival Telstra Corp Ltd has disclosed a small breach of employee data, while No. 1 grocery chain Woolworths Group Ltd said an unidentified party gained unauthorised access to the customer database of a bargain website used by 2.2 million shoppers.

Additional reporting by Reuters