In response to a query from iTWire, a spokesman said on Tuesday: "Fortunately, our recovery process is progressing and our ability to deliver care to our patients and support our clinicians has not been compromised."

The breach was staged by a ransomware gang known as Hive that only attacks systems running Microsoft's Windows operating system.

In a fresh advisory, MHC added: "Thank you to our staff for their hard work continuing to deliver patient-centred care with many of our systems remaining off-line.

The Hive gang, which claims to have encrypted the MHC files on 25 September, has not said anything on its website to indicate whether it has approached MHC to negotiate a ransom.

Hive has been described as a double-extortion ransomware group — "making their money off of a two-pronged attack: exfiltrating sensitive data before locking up the victims’ systems" — that first made its presence known in June this year.

Jim Walter and Juan Andres Guerrero-Saade of security shop SentinelLabs said in a blog post about Hive in August: "The group is notable in its undiscerning choice of targets, having no limits when it comes to healthcare providers and hospitals, as evidenced in a recent attack on Memorial Health System hospitals in Ohio.

"Hive ransomware is written in Go to take advantage of the language’s concurrency features to encrypt files faster. Hive remains active with as many as 30 victim companies listed on its Hive Leaks onion site at the time of writing."

Macquarie Health has 12 hospitals which provide surgical procedures, rehabilitation and mental health clinics, skin imaging and dermascopy, medical systems; cosmetic procedures, e-health informatics and data solutions.

The units under its banner are Macquarie Hospital Services, MacRehab, Macquarie Medical Systems, Derma Medical and Machealth eSolutions.

Commenting on the incident, Aparna Sundararajan, [above, right] senior research strategist at specialist research and advisory firm ADAPT, said: "This breach is a reminder that regardless of sector, all organisations are vulnerable to serious security breaches, and will find themselves under attack at some point.

"Ransomware has been the number one cyber security concern for Australian digital leaders over the past few years, and we expect to see threats grow in number and sophistication as criminals target healthcare organisations, often seen as a treasure trove of high-value personal information.

"With healthcare deemed 'Critical Infrastructure' by the Federal Government, we can expect to see tighter cyber security regulation in the future. This will give organisations an even greater imperative to minimise the risk of these attacks.

"To reduce the threat posed by ransomware, security leaders should focus on identifying the most strategic data assets, define an isolation strategy, and adopt measures that offer quick recovery without interrupting normal operations. We have the technology to do so, but it's the security culture at the top that needs prioritising right now.

"We need an open dialogue between organisational leaders and their security teams to build an adequately-funded cyber resilience strategy. Security is everybody's business, and that mindset will help a lot more than holding a small group of people responsible for it all."

Ransomware researcher Brett Callow, who works for the New Zealand-headquartered security shop Emsisoft, told iTWire that ransomware attacks on healthcare providers were insidious.

"They have the potential to impact patient care, possibly resulting in the loss of life. And that's especially true during a pandemic," he added, referring to an article about this on the US site, The Verge.