Australian police last week made 55 arrests using evidence gathered with a backdoored messaging app that authorities distributed in the criminal community.

This story starts in 2018, when US authorities charged the operator of a Canadian company called “Phantom Secure” for facilitating encrypted communications among criminals. Once Phantom Secure went offline, authorities guessed that criminals would look for alternatives.

The FBI, working with Australia’s Federal Police (AFP), created that alternative in the form of a service called “AN0M” that ran on modified smartphones and required users to pay subscription fees for a secure communications service. AN0M also included a backdoor that allowed authorities to access messages sent using the service.

Crims didn’t know about the backdoor and merrily used AN0M to discuss many evil deeds.

In 2021, amid a flurry of arrests around the world, the AFP revealed the existence of AN0M and “Operation Ironside” that used intelligence gathered from the app to investigate criminals.

In 2022, some AN0M users who faced criminal charges tried to challenge the legality of the scheme, which they argued amounted to unlawful interception of communications passing over a telecommunications network under Australian law. In early October, Australia’s High Court found [PDF] AN0M was legal because it was a closed system, and messages sent with the app therefore didn’t go across a telecoms network.

The litigants can’t appeal that decision because Australia’s High Court is the nation’s ultimate jurisdiction.

Last week, police in the Australian State of South Australia (SAPOL) SA Police raided 23 properties, arrested and charged 55 people they allege were “involved in serious and organised crime,” and “restrained” assets valued at AUD$25.8 million ($17 million). SAPOL’s announcement noted the presence of two Harley Davidson motorcycles among the restrained assets, a likely hint to the affiliation of some of those arrested.

SAPOL said the raids represent “the latest phase of Operation Ironside” and a “third tranche” of activity connected to AN0M.

The AFP and FBI stopped using AN0M because it produced more evidence than they could comfortably handle. The AFP, however, still wants access to encrypted communications and last year called for operators of encrypted messaging services to practice “accountable encryption” to help authorities quickly investigate messages felt to represent a threat to safety and security. ®