By Dominic Giannini in Canberra

Social tensions over hotbed issues such as the war in Gaza amplified by divisive social media have heightened the risk of a violent attack in Australia.

ASIO increased the terror threat level from “possible” to “probable” after the intelligence agency’s chief revealed eight attacks or disruptions that involved alleged terrorism had been investigated in the past four months.

The decision to heighten the threat level was not due to a specific incident and while tensions in the Middle East meant strains in Australia, they had not directly contributed to the increase, Mike Burgess said.

Australian Strategic Policy Institute executive director Justin Bassi pointed to a trend of increasing numbers of people being radicalised on short notice due to numerous factors.

These included religious extremism and grievances, resentments and conspiracy theories that fall under the umbrella of anti-authority ideologies, the former national security advisor to prime minister Malcolm Turnbull said.

“These range from economic grievances to hatred of immigration to conspiracy theories about traditional institutions, shown in views such as anti-vaxxer stances,” he said.

“They are amplified and energised through social media.”

Lockdowns during COVID-19 prompting children to spend more time on screens, resulted in half of ASIO’s cases being minors, Mr Burgess said.

“It is a concern how social media can grab people quickly, the internet can grab people quickly and hurt young brains which are not fully formed,” he told ABC TV.

“You could fall down a rabbit hole of hate quickly.”

Lone-wolf terror attacks with little warning and simple weapons such as knives were a major threat, the spy chief said.

Of the eight cases since April, only two were known to police or intelligence services, he said.

“People will go to violence with no warning,” he said.

“(The cases) are symptomatic of what we are seeing in society with increased temperature, violence is more permissible.”

One person investigated had latched onto the extreme left-wing Antifa but had neo-Nazism in a manifesto, Mr Burgess revealed.

“That defies logic, I would suggest they are not really hooked on either of those ideologies, they are hooked on the violence element,” he said.