Indian and French authorities will launch an investigation into the reported leak of documents related to Scorpene submarines.
The suspected data leak, containing more than 22,000 pages, was first reported by The Australian newspaper.
The leaked documents describe the combat capability of six submarines, which were designed by French shipbuilder DCNS for the Indian Navy as part of a $3bn deal, Hindustan Times reported.
The Indian Ministry of Defence said that the source of the leak is believed to be from overseas.
It also stated that the available information is being examined at the Integrated Headquarters, Ministry of Defence (Navy), and an analysis is being carried out by the concerned specialists.
Indian Defence Minister Manohar Parrikar was quoted by media sources as saying: "I understand there has been a case of hacking.
"We will find out what has happened."
The leak has raised fears in Australia, as DCNS has been awarded a A$50bn ($38.06bn) contract to build submarines for the country.
DCNS Australia spokeswoman said: "As a serious matter pertaining to the Indian Scorpene programme, French national authorities for defence security will formally investigate and determine the exact nature of the leaked documents.
"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."
Similar submarines are currently in service in Malaysia and Chile.