One of the world’s top cyber-security experts says the biggest threat facing Australia is the US.

French-born, Sydney-based Jonathan Brossard, whose stable of clients includes the Commonwealth Bank and European car manufacturers, says the US may be a close ally but it would wrong to think the US was not spying on Australia.

‘‘They are the biggest threat,’’ the chief executive of Toucan System said.

‘‘Australia is part of the Five Eyes and all that and there is a strong belief that allies are not spying on us.

‘‘I think that’s pure bulls--- ... I think we are completely owned by the Americans," he said.