French shipbuilder DCNS has been hit by a massive data leak affecting a major submarine contract for the Indian navy.
The leak of more than 22,000 pages exposes detailed information about the combat capability of the Scorpene class vessels.
It is not clear who first obtained the confidential documents, which were made public by the Australian media.
Earlier this year DCNS won Australia's largest-ever defence contract to build a fleet of advanced submarines.
Details about the Shortfin Barracuda submarine class that will be built for Australia were not contained in the leak.
A DCNS spokeswoman described the leak as "a serious matter" and said French authorities would formally investigate.
"The matters in connection to India have no bearing on the Australian submarine programme, which operates under the Australian government's arrangements for the protection of sensitive data," a statement said.
India signed a $3.5b (£2.6b, €3.1b) deal for six Scorpene vessels in 2005. They are to be built in cooperation with an Indian government-owned shipbuilder in Mumbai.
The Scorpene submarines are small-to-intermediate size vessels currently in use in Malaysia and Chile. Brazil is due to deploy the submarine type in 2018.
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.
The Shortfin Barracuda submarines are to be built in Adelaide with the expectation of creating around 2,800 jobs in the region.
They will be 4,500-tonne conventionally powered submarines, closely related to the nuclear-powered Barracuda, which weighs 4,700 tonnes.
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.
The country's defence industry minister, Christopher Pyne, said in a statement that the leak had "no bearing on the Australian government's future submarine programme".