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.

’’Five Eyes is the intelligence alliance between Australia, the US, UK, Canada and New Zealand"

Mr Brossard is one of the world’s best-known ‘‘ethical hackers’’, and uses his computer skills to help companies strengthen their cyber security.

‘‘I have been working with the Commonwealth Bank for two years,’’ he said. ‘‘On a daily basis my job was to rob the bank and then give the money back.’’

Australia, generally, ‘‘is pretty good’’ in terms of cyber security, although Brossard said a problem Australia, Europe and the US faced was that most technology was built in Asia.

‘‘If we are not building it, we have no idea if it is actually secure,’’ he said.

‘‘Not only if it has been built properly, but how do we make sure it has not been 'backdoored?' We need to go back and do our own hardware and write our own software. We are very dependent on foreign nations that in other respects we don’t trust very much.’’

Mr Brossard was speaking in Chicago, where he was helping to launch Ubisoft’s new action-adventure video game, Watch Dogs.

The game, which took five years to create, is set in Chicago and centres on a computer hacker who has to break into surveillance networks, mobile phones and other electronic systems.