The use of WhatsApp is not limited to senior ministers; private chat 'groups' exist for government chiefs of staff, ministerial media advisers, the frontline economic team, and a defence-focused "broadcast group" used by Defence Industry Minister Christopher Pyne to communicate with MPs and staff.

Fairfax Media has spoken with four cyber security experts who have each flagged potential security issues with the widespread use of WhatsApp by the Turnbull government – particularly at a cabinet level – in place of secure, government email servers from platforms approved by the Australian Signals Directorate (ASD), Australia's cyber intelligence agency.

Craig Searle, the founder of security consultancy firm Hivint, pointed out WhatsApp was not an approved platform on the ASD list of Evaluated Products or Certified Cloud Services, whereas Apple's iOS operating system and Blackberry's operating system were.

"Should government be using secure messaging apps? Yes, they are a great idea. But for government staff in particular, they have to be cognisant of data classification requirements, they should behave securely and use products on the Australia government's certified list," he said.

"If a government employee were to transfer classified data across a non-approved app or network, that could be a potential security breach."

WhatsApp has a user base of about one billion people and can be used to send one-to-one and group messages, video and make phone calls. It is owned by Facebook, with which it recently began to share more user data.

Multiple government staff confirmed to Fairfax Media the platform was widely used within the government, including by a group of cabinet ministers.

"I can't imagine ASD is very happy about it," one staffer said.

A government spokesman said the WhatsApp groups were designed to improve internal government communication and coordination.

The spokesman did not deny a cabinet-level group existed but said secure information such as classified, sensitive and "not for release" material was handled in the appropriate way.

"The government uses many channels of communications, including WhatsApp," he said. "All classified communications happen appropriately on secure channels. There is a protocol around the security of mobile devices."

But Australian Strategic Policy Institute cyber security expert Tobias Feakin said despite WhatsApp trumpeting end-to-end encryption – which secures a message once it is sent from one phone, via a server, to another phone – risks remained.

"The risk of WhatsApp is at either end of the cycle, on the sending device or receiving device. People can misplace a device and then it can potentially be accessed. Then there is phishing – someone clicking a link or opening an attachment [in the app] which downloads software," Dr Feakin said.

"The headache for government is that this is a platform that rests outside government's purview and that therefore poses some security risks."

Queensland University of Technology security expert Emeritus Professor Bill Caelli said cabinet communications should happen on a secure device or not at all.

"If it's not on ASD's list ... the answer is 100 per cent no."

University of Canberra director of internet safety Nigel Phair said "of course" cabinet ministers should not use WhatsApp.

Mr Turnbull's love of new technology like the Apple Watch and communications platforms including WhatsApp and Wickr is well known. Soon after becoming Prime Minister he reportedly suggested to cabinet colleagues they use messaging app Slack to stay in touch, a direction that baffled some colleagues.

One senior staffer said WhatsApp is "Malcolm's favourite thing, so everyone jumped on it" when he became Liberal Party leader in September 2015.

US presidential candidate Hillary Clinton has faced months of criticism after it emerged she used a private email server while Secretary of State, a revelation which sparked a criminal investigation by the FBI and repeated attacks by Republicans and rival Donald Trump. Emails recovered from Mrs Clinton's accounts and released by the US government have been the subject of intense media attention.

The use of the app also raises questions about whether the communications are covered by Australia's Freedom of Information laws because the content of the messages are not stored on government servers – as emails are – but instead exist on an individual's phone.

Department of Prime Minister and Cabinet deputy secretary Allan McKinnon advised Mr Turnbull in October 2015 that messages sent on third party platforms such as WhatsApp should be covered by FOI laws.

However in a subsequent Senate hearing Mr McKinnon confirmed the government could not, for example, search for messages sent on the Wickr or Slack platforms, which function in a similar way to WhatsApp.

Comment was sought from the Australian Signals Directorate.

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