Earlier this year DCNS won Australia's largest-ever defence contract to build a fleet of advanced submarines.
DCNS beat out strong competition from Germany and Japan to secure Australia's A$50bn (€34bn; £27bn) contract to build its navy's next generation of submarines, a project that will stretch into the 2050s.
Australian Prime Minister Malcolm Turnbull said the leak was a reminder of the importance of Cyber Security, but rejected concerns it would endanger the contract.
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