Here is your 10-point cheat-sheet to this story:
"What I understand is that there has been a hacking... the first important thing is to identify if it is related to us," the Defence Minister said after an Australian newspaper reported the leak. Mr Parrikar said that he had learned about the leak at midnight yesterday, and that he expected details in a couple of days.
Newspaper The Australian has said it has accessed 22,400 leaked pages, marked "Restricted Scorpene India", of what is essentially the operating manual of the submarine, designed by French defence contractor DCNS for the Indian Navy.
The first of six submarines, the INS Kalvari, is now being built at Mumbai's Mazgaon Docks.The submarines are considered some of the most advanced of their class in the world, so silent under water that they are extremely difficult, if not impossible to detect.
The classified data now out in the open includes thousands of pages on the submarine sensors and thousands more on its communication and navigation systems as well as nearly 500 pages on the torpedo launch system alone.
The Australian reports that DCNS has implied that the leak may have come from India, but the daily said the data was thought to have been removed from France in 2011 by a former French navy officer who at the time was a subcontractor for DCNS.
The data is believed to have passed through firms in Southeast Asia before eventually being mailed to a company in Australia, the newspaper said.
DCNS has said it has launched an inquiry which "will determine the precise nature of the documents which have been leaked, the potential damage to our customers as well as those responsible."
DCNS also said on Wednesday that it could not rule out that leaked documents on submarines built for India were part of an "economic war" by competitors after the firm won a tender in Australia earlier this year. "The competition is more and more hard and all means can be used in this context," a DCNS spokeswoman said.
Meanwhile, the Congress has demanded a "high-level inquiry" into the leak. "It is the serious matter, it affects the security of the country. The government must find out the truth and then we can consider future course of action.
Variants of the submarine are used by Malaysia and Chile. Brazil is also due to deploy the vessels from 2018. Australia has awarded a submarine contract to DCNS, but the secret combat system for the 12 Shortfin Barracudas is being supplied by the United States.
Indian Navy's Top Meet Amid Bangladesh Crisis, China's Aggressive Tactics Indian Navy Invites Applications For Sailors In Medical Branch, Check Details Indian Navy's P8i Poseidon Aircraft Reaches France, 1st-Ever Deployment In Europe 1000s Of Pagers Explode Across Lebanon, Several Hezbollah Members Injured IndiGo Flight Tailstrike Leaves Huge Dent During Take-Off From Delhi Airport Video: Leopard Spotted Crossing Road In Bengaluru's Electronic City Instagram Rolls Out "Teen Accounts" With Parental Control For Underage Users All You Need To Know About Atishi, Set To Be Delhi's Youngest Chief Minister IndiGo Flight Tailstrike Leaves Huge Dent During Take-Off From Delhi Airport Track Latest News Live on NDTV.com and get news updates from India and around the world.