It comes as Canberra experiences its second week of anti-vaccination mandate protests, pushing for governments to dump vaccine requirements for specific industries and compensate those who have lost jobs as a result of them.

Australian Security Intelligence Organisation director-general Mike Burgess said COVID lockdowns had pushed more people online, exposing some to radical and fringe views without the usual "circuit breakers" of life.

In his annual threat assessment, delivered on Wednesday evening, Mr Burgess said the internet was the "world's single most potent and powerful incubator of extremism".

"Social media platforms, chat rooms, and algorithms are designed to join up people who share the same views, and push them material they will 'like'," he said.

"It's like being in an echo chamber where the echo gets louder and louder, generating cycles of exposure and reinforcement."

However, the agency said it was focusing on a small number of "angry and alienated Australians" who were more prone to violence.

Many of those who had expressed anti-vaccination mandate views were newcomers, leaving the agency's analysts with tough judgement calls to make.

"They are a cocktail of views, fears, frustrations and conspiracies," he said.

"In this uptick in specific-issue or grievance-motivated violent extremism, many of the actors are newcomers, so it's harder to get a sense of what is simply big talk-and what is genuine planning for violence."

Those involved in recent anti-vaccination protests in the nation's capital, including demonstrations at Old Parliament House that led to its front door being set alight, were "driven by a diverse range of grievances".

Anti-vaccination agendas, conspiracy theories and anti-government sovereign citizen beliefs formed the protesters' coalition with racist and nationalist supporters forming a small part of the larger group.

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Mr Burgess expected them to continue for the years ahead as vaccine requirements are introduced for some jobs and travel, driving "anger, uncertainty and fear within a small section of society".

"Protests driven by diverse specific-issue grievances will be part of our security environment for the foreseeable future," he said.

"In some cases, protesters will advocate the use of violence, and in a smaller number of cases, they may use violence."

The intelligence head said the most likely terrorist attack scenario in Australia over the next 12 months continued to be a lone-actor attack.

A sharp rise in the number of minors forming the agency's counter-terrorism investigation case load represented another growing threat.

Mr Burgess said minors made up around 15 per cent of its new investigations compared with around 2 or 3 per cent years earlier.

By the end of last year, he said minors had started to represent more than half of priority counter-terrorism investigations each week.

Young radicalised violent extremists had taken it upon themselves to target and recruit lonely peers to their causes both online and in school settings.

ASIO said it did not belong in the schoolyard and needed governments, in conjunction with schools, sports clubs, parents and carers, to intervene and support in these cases.

"As a nation, we need to reflect on why some teenagers are hanging Nazi flags and portraits of the Christchurch killer on their bedroom walls, and why others are sharing beheading videos," he said.

"Perhaps more disturbingly, these young people are more intense in their extremism.

"Where once minors tended to be on the fringe of extremist groups, we are now seeing teenagers in leadership positions, directing adults, and willing to take violent action themselves."

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