The main online portal for lodging tax returns is back up and running again after crashing for more than six hours on Friday.

The site crashed from about 10am to 3pm – the same day the federal government was due to pay more than $1 billion into taxpayers’ bank accounts.

The Australian Taxation Office said the myGov website breakdown was “unrelated” to the surge of tens of thousands of people rushing to cash in on recently legislated tax cuts.

The glitch prevented people from lodging their tax returns and cut them off from critical services such as Centrelink, Medicare and child support.

It is not the first time, however, that vital government-run online services have plunged taxpayers into chaos.

Last year in November, a helpline to opt out of the controversial My Health Record system crashed over a “technical issue” after thousands rushed to opt out before the deadline.

In 2016, Centrelink’s computer-generated system accidentally sent hundreds of thousands of debt notices demanding money from people who did not owe anything, or owed much smaller debts.

It has since emerged that more than 2030 people died after receiving a Centrelink ‘robo-debt’ notice, according to data released by the Department of Human Services.

In another incident in 2016, the Australian Bureau of Statistics was forced to apologise after a mass outage of the census website stopped thousands of people around the country from completing the survey online for the first time.

What caused the myGov website to crash?

Cyber security expert Andrew Woodward said the myGov glitch could have been caused by a number of factors, including a cyber attack, a technical failure or a simple human mistake.

“We all remember the census debacle,” Professor Woodward told The New Daily, pointing to the 2016 #Censusfail disaster.

However, he said rather than simply blaming the federal government for the myGov portal breakdown, it was important to recognise how easy it was for someone to launch a cyber attack on big online systems.

“When you have a big front-facing web service, it can be really tricky to block a cyber attack,” Professor Woodward said.

“In some part it comes down to the massive skills shortage in Australia – there aren’t enough cyber security professionals to go around helping people adequately secure everything.”

Cyber security researcher Paul Haskell-Dowland said while it was too early to tell the exact cause of the system failure yet, “it doesn’t take much for a cascade effect”.

“We depend on this technology, and a lot of people have different requirements offered through the myGov website,” Professor Haskell-Dowland said.

“No one is going to be drastically affected by not being able to lodge their tax returns today, but individuals could have been really inconvenienced by their inability to access services such as their My Health records.”

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