Legal challenges are being launched after criminals around the world were brought down by a fake messaging app. 

Dozens of people charged as part of one of the world's largest police operations are questioning the admissibility of evidence obtained during the investigation. 

Over 50 people were in court for a landmark committal hearing this week, challenging the evidence obtained from the AN0M app, the crucial source of evidence used by investigators involved in Operation Ironside. 

AN0M, an app run by the US Federal Bureau of Intelligence (FBI) and decoded by the Australian Federal Police (AFP), led to the arrest of over 250 alleged organised crime figures across Australia in 2021. 

The app was a ‘Trojan horse’, a black-market phone that was passed around the underworld from 2018 in the belief that it was off the police radar. The phones were seeded by police, and every message, voice note, or picture sent on the platform was automatically duplicated.

In June 2021, AN0M was shut down, and hundreds of alleged gangsters across the globe were arrested. 

The investigation was known as Operation Ironside in Australia and Trojan Shield in the US. 

The AFP alleged evidence gained through surveilled texts allowed police to bring down drug supply rings and organised crime networks in Australia and overseas.

During the committal hearing before Magistrate Robert Williams, the group of alleged bikies and criminals' lawyers explored whether the evidence was legally intercepted. 

Barristers Avni Djemal SC and Phillip Boulten SC represented various accused parties, while Christopher Winneke KC acted for state and federal prosecutors. The group is challenging whether the duplication of messages was legal.

Yogesh Khatri, a forensic investigator with cybersecurity firm CyberCX, provided evidence at the hearing. 

He was able to explain how the app worked from a technical standpoint, having been given access to some of AN0M's source codes. 

Much of the questioning from Mr Djemal focused on the point at which the duplication took place and whether the phones were connected to a "telecommunications network" at the time. Khatri said they were.

In a similar challenge, Justice Adam Kimber in the Supreme Court of South Australia ruled that AN0M was legally run by police. The committal hearing continues in NSW with 14 witnesses to give evidence over the ten-day hearing.