An Australian man has pleaded guilty in connection with a scheme to steal powerful hacking tools from an American defence contractor and sell them to a buyer in Russia, the US Justice Department said.

The tools were "meant to be sold exclusively to the US government and select allies," but 39-year-old Peter Williams sold them to a Russian software exploit broker that touted its ties to Moscow and other foreign governments, the Justice Department alleged.

Prosecutors say the theft caused $US35 million ($53 million) in losses for the company, which is not identified in court documents.

But British business records list Williams as the former general manager of Trenchant, an intelligence firm owned by US defence contractor L3Harris Technologies.

L3Harris' website describes Trenchant as a

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