And an intelligence agent assuming a false identity convinced an aspiring Islamic terrorist to abandon plans to wage a holy war, it has been revealed.

The head of Australia's foreign intelligence and cyber security agency has lifted the lid on the top-secret operations as he kick-starts a recruitment drive.

Australian Signals Directorate director-general Mike Burgess has revealed that his officers helped shape a crucial battle at the height of the fight against Islamic State.

Just as coalition forces were preparing to attack the militants, his team were at their keyboards in Australia, disabling the extremist group's command and control networks.

"Daesch communications were degraded within seconds," Mr Burgess will tell the Lowy Institute in Sydney on Wednesday.

"Terrorist commanders couldn't connect to the internet and were unable to communicate with each other.

"The terrorists were in disarray and driven from their position - in part because of the young men and women at their keyboards some 11,000 kilometres away."

It was the first time an offensive cyber operation had been conducted so closely alongside military officers in the field.

"Without reliable communications, the enemy had no means to organise themselves, and the coalition forces regained the territory," Mr Burgess said.

The ASD has also been used to damage the terrorist group's media machine, undermining its ability to spread hateful propaganda and recruit new members.

Mr Burgess also revealed how one of his operators tracked down a man who had been radicalised and was trying to join a terrorist group overseas.

The young woman, a science graduate, posed as a terrorist commander to win the target's trust.

Using broken English, she eventually convinced the man to abandon his plans for jihad and move to another country, where partner agencies ensured he was no longer a threat.

"In this case, a young operative sitting at a computer in Canberra successfully pretended to be a senior terrorist fighting in a faraway war zone," Mr Burgess said.

"One word or reference out of place and the whole thing could have fallen apart, potentially with grave consequences."

Mr Burgess said the operator had done extraordinary work, but had a fairly ordinary background.

She grew up in the suburbs and enjoys yoga, hiking and touch football.

"And when she was studying science at university, she would never have dreamed that one day she would be posing online as a terrorist, and helping to defend Australia from global threats," he said.

Mr Burgess, who famously brought the ASD "out from the shadows" during a major speech last year, is now shining a light on the agency's offensive cyber capabilities to aid a recruitment drive.

The intelligence agency is trying to shake the perception it is only in the market for male computer geeks, pointing out that some of its best covert online operators are women from diverse non-IT backgrounds.

Australian Associated Press