About 12.9 million Australians had their data stolen in the MediSecure hack earlier this year, the eScripts provider has revealed, placing it among the largest cyber breaches in Australian history.

MediSecure, which facilitates electronic prescriptions and dispensing, confirmed in May it was the victim of a ransomware attack, although the theft itself took place earlier, and continued until November 2023.

The company had not previously disclosed how many Australians were affected, and has not contacted people individually.

Medisecure was one of only two eScript providers in Australia until late last year, when competitor eRx took over the government contract to supply the entire market.

The company went into voluntary administration in June after the federal government declined to provide it with a financial bailout.