A crippling outage that caused nationwide disruptions to transport networks, business, emergency services and healthcare has exposed the vulnerability of Australia’s critical infrastructure to telecommunication faults.

Australia’s largest telco blamed a software defect for an hours-long outage that affected millions of phone-users, travellers and shoppers on Wednesday.

Network problems left users unable to make calls or access data on their mobile phones, while some EFTPOS transactions were also impacted.

It is the third major national outage in less than a year for the $56 billion giant, which powers about 25 million Australian mobile services.

It is a reminder of how reliant our critical infrastructure is on telecommunications providers, experts say.

The incident exposes the fragility of the infrastructure Australians depend on for the most basic transactions, Griffith University competition and retail expert Graeme Hughes said.

“(Wednesday’s) outage shows that the question is no longer whether Australians can make phone calls, but whether the economy can function when a single network fails,” he said.

“Within hours, Victoria’s regional rail network was suspended, payment terminals serving roughly 80,000 businesses were disrupted, and taxi passengers were left unable to pay their fares.

“None of this required a cyberattack. It required a single technical fault at one carrier.”

The lesson for policymakers, he said, was that mobile connectivity is crucial economic infrastructure and must be regulated as such.

Telstra said potential triple-zero call problems were more widespread than previously thought, requiring hundreds of welfare checks.

‘Great risk’

Telecommunications expert and RMIT Associate Professor Mark Gregory said the telecommunications legislation was written in the 90s and did not reflect the modern, digital world.

“We’ve got a structural problem with systemic failures built into it,” he told AAP.

“The legislation needs to be rebuilt structurally from the ground up and brought into tune with the modern era and it needs to be focused around the customer.”

La Trobe University Professor Daswin De Silva said the Security of Critical Infrastructure Act 2018 - which covers telecom providers as one of 11 critical infrastructure sectors - needed further government oversight and accountability measures.

“Telecommunications is one of our critical infrastructure sectors that has systemic impact across the economy, society and national security, including emergency services and healthcare, to banking and transport networks,” he said.

Although Telstra chief financial officer Michael Ackland unequivocally denied the outage could have been the result of a cyberattack, cybersecurity expert Dennis Desmond said the incident exposed the vulnerability of critical infrastructure.

“Whether due to adversarial attack, internal equipment failures, or patches and upgrades to firmware or software, our reliance on our critical infrastructure places Australian citizens and the services they receive at great risk,” he said.

“If attributed to nefarious actors rather than internal errors or failures, the long-term effects could be much more severe than we experience with temporary outages.”

Investigations into the underlying cause of Telstra’s software glitch are ongoing.