Louise Milligan claims Redfield College alumni 'threatened' her over ABC Four ... trends now

ABC host Louise Milligan has hit back at a mystery high school graduate from a 'prominent family' after he allegedly threatened her over her investigation into an ultra-conservative Catholic group and its alleged links to schools.

The Four Corners journalist revealed on Monday her safety had been 'threatened' by a graduate of Redfield College in Dural, north-west Sydney.

The private college is one of several schools named in an upcoming Four Corners investigation that will air on the public broadcaster on Monday night.

The segment will explore the different schools and their close link to the Catholic offshoot Opus Dei and serious allegations of 'disturbing practices' in the classrooms.

Misinformation about sexual health, homophobia, opposition to consent education and encouraging girls to not get the HPV vaccine are among the accusations former students have made about the schools. 

Milligan said she had made a report to police after receiving the threatening message from the Redfield College graduate.  

'To the 2021 old boy of Redfield College from a prominent family who threatened my safety on social media ahead of our investigation into his alma ahead of tonight's Four Corners, police are investigating,' she wrote on Twitter.

'You cannot threaten women. Enough. I trust the school will assist NSW Police.'

She added in another series of tweets: 'I should add that I have never met this person. 

'And that when he sent these despicable threats, he had not seen any of our story. And of course I mean alma mater.'

Daily Mail Australia contacted NSW Police who said Victoria Police would likely handle the investigation given Ms Milligan lives in Melbourne. 

Victoria Police said it could not comment on specific individuals out of privacy.