The Ghost app was marketed to underworld figures as "unhackable" and used by hundreds of suspected criminals from Europe, the Middle East, Australia and Asia.

It was allegedly designed by a 32-year-old Australian computer whiz living with his parents in suburban Sydney.

The Australian Federal Police said Wednesday they had arrested a 47-year-old man "alleged to be a distributor" of the app.

Encrypted phones were pre-loaded with Ghost before the man stashed them at "dead drops", or pre-arranged hiding places for collection, police said.

Global policing authorities managed to infiltrate the network, watching as criminals discussed illicit drug trafficking, money laundering, homicides and serious violence.

Police swooped in September, arresting criminals from Italy, Ireland, Sweden, Canada and Australia -- including Jay Je Yoon Jung, the alleged "mastermind".

Ghost, a kind of WhatsApp for criminals, was created nine years ago and could only be accessed via modified smartphones that sold for about Aus$2,350 (US$1,590).

French police traced the creator's location to Australia and joined forces with local police to target the platform.

Several thousand people worldwide used Ghost and around 1,000 messages were exchanged on it every day, according to Europol.

There were 376 phones with the Ghost app installed in Australia alone.