This was the latest in a series of hacks targeting millions of people that have brought Australian companies' lax approach to cyber security into sharp relief."Our investigation has now established that this criminal has accessed all our private health insurance customers' personal data and significant amounts of their health claims data," he said in a statement to the Australian stock exchange.The hackers have previously threatened to leak the data, starting with 1,000 famous Australians, unless Medibank pays a ransom.Medibank on Wednesday also confirmed it was not insured against cyber attacks, estimating the hack could cost the company as much as Au$35 million (US$22 million)."Unfortunately, significant privacy breaches in recent weeks have shown existing safeguards are inadequate," he said."