It comes after the Australian government, with support from Medibank, refused to pay a ransom for the data.
The public was urged by Medibank not to look for the files because they contain the names of policyholders rather than patients.
David Koczkaro, CEO, issued a warning that the data release might discourage people from seeking medical care.
Numerous factors, such as complications, miscarriages, and non-viable pregnancies, can lead to abortions.
The misuse of their data is abhorrent, and it might deter them from seeking medical attention. “These are real people behind this data,” he said.
The latest in a series of significant data breaches at Australian businesses in recent months involved the theft of 9.7 million Medibank customers’ personal information.
The hackers released their first batch of data this week after Medibank refused to pay a $10m (£8.7m; A$15.6m) ransom — roughly $1 for each client — demanded by the hackers.
Some Australians claim that after their medical information was posted online, scammers started to target them.
Todd Woodbridge, a former tennis champion who is recovering from a heart attack, claimed he had received a constant stream of calls from con artists who knew which hospital he had been in.
He told Melbourne radio station 3AW on Wednesday, “I think I’m one of those people who have been scammed by the Medibank situation; I’m a customer of theirs.”
Medibank has come under fire from him and others for the security lapse.
The hackers published a set of customer information files titled “good-list” and “naughty-list” earlier this week.
The files contained information on individuals’ health claims, such as medical procedure histories, as well as names, addresses, birthdates, and government identification numbers.
The hackers later added: “added one more file abortions.csv” to their forum on Thursday.
Medibank has issued an apology for what it has referred to as the “malicious weaponization” of personal data. The information was obtained by the hackers after login credentials giving them access to all of its customer data were stolen.
The company’s decision to refuse to pay the ransom was also defended by the Australian government.
Both have issued warnings about the likelihood of additional customer data releases. Anthony Albanese, the prime minister, has acknowledged that he uses Medibank as well.
The second-largest telecommunications company in Australia, Optus, was also the target of extortion in September after the company reported that a cyberattack had resulted in the theft of the personal information of about 10 million customers.
Many Australians who have been impacted by both breaches have come forward.
According to local media, the ransomware group REvil’s blog has posted the stolen Medibank data.