(Reuters) — Medibank Private Ltd., Australia’s biggest health insurer, said Wednesday a cyber hack had compromised data of all of its nearly 4 million customers, as it warned of a A$25 million to A$35 million ($16 million to $22.3 million) hit to first-half earnings.
It said that all personal and significant amounts of health claims data of all its customers were compromised in the breach reported this month, a day after it warned the number of customers affected would grow.
Shares in the company fell more than 14%, its biggest one-day slide since listing in 2014.
Medibank, which covers one-sixth of Australians, said the estimated cost did not include further potential remediation or regulatory expenses.
Medibank CEO David Koczkar said in a statement. “I apologize unreservedly to our customers. This is a terrible crime – this is a crime designed to cause maximum harm to the most vulnerable members of our community.”
The company reiterated that its IT systems had not been encrypted by ransomware to date and that it would continue to monitor for any further suspicious activity.