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The man accused of selling secrets to Russia worked for the Australian Signals Directorate, which is responsible for cyber security. (Four Corners: Cyber War)

An Australian man who was working for a US-based defence and cyber intelligence contractor has been accused of selling information to a Russian buyer.

Multiple sources have told the ABC the accused man used to work for the Australian Signals Directorate, the national intelligence agency responsible for cyber security.

The man's case is due to return to a US court overnight.

An Australian man in the United States who has been accused of selling trade secrets to a Russian buyer for almost $2 million used to work for Australia's signals intelligence agency.

US prosecutors have alleged in court documents that Peter Williams — who worked for a US-based defence and cyber intelligence contractor — sold eight "trade secrets" to a "buyer based in the Russian Federation" between April 2022 and August 2025.

The documents do not provide any details of the trade secrets which Mr Williams is alleged to have sold.

Multiple sources have told the ABC that Mr Williams worked for the Australian Signals Directorate (ASD) in the 2010s — although the ABC has not been able to establish exactly when he left the organisation, or when he moved to the United States.