Australia's top spy agency says it looked at the security implications of a pandemic as far back as 2007.
ASIO boss Mike Burgess said in his annual threat assessment speech on Wednesday the finding from 15 years ago was a pandemic would see a rise in anti-government behaviour.
"And we have certainly seen that with COVID," he said.
Mr Burgess said the pandemic had had a number of impacts.
One was an increase in radicalisation and "specific-issue grievance", which in a small number of protester cases had turned to violence.
"We have seen threats against public office holders, an attack on a vaccination clinic, and several physical assaults on healthcare workers," he said.
"We assess that these tensions and the associated possibility of violence will persist."
As well, COVID-19 lockdowns had led to people spending more time online, putting them at risk of radicalisation.
"Online radicalisation is nothing new, but COVID-19 sent it into overdrive. Isolated individuals spent more time online, exposed to extremist messaging, misinformation and conspiracy theories," Mr Burgess said.
"More time in those online environments - without some of the circuit breakers of everyday life, like family and community engagement, school and work - created more extremists.
"And in some cases, it accelerated extremists' progression on the radicalisation pathway towards violence."
Mr Burgess said minors now represented around 15 per cent of new counter-terrorism investigations and their extremism was more intense.
"Children as young as 13 are now embracing extremism, and this is happening with religiously motivated violent extremism and ideologically motivated violent extremism," he said.
"And unlike past experience, many of these young people do not come from families where a parent or sibling already holds extreme views."
He said sports clubs, schools, parents, carers and community leaders could play a pivotal role in identifying signs of teenagers heading towards radicalisation.
"The acceleration of radicalisation, online propaganda and misinformation, single-issue extremism and minors embracing violent extremism all require a whole-of-government, whole-of-system and whole-of-nation approach."
