Details of India's stealth submarines leaked online

File photo of Indian Navy's Scorpene submarine INS Kalvari being escorted by tugboats as it arrives at Mazagon Docks Ltd, a naval vessel ship building yard, in Mumbai, India, Oct. 29, 2015. (REUTERS/Shailesh Andrade/Files)

If there's one thing you don't want to lose, it's confidential information about a high-tech fleet of submarines.

But that's what happened to the Indian Navy, which is investigating the leak of 22,000-plus pages of documents revealing data about its Scorpene subs.

"What I understand right now is that there is a case of hacking," Indian Minister of Defense Manohar Parrikar told reporters today, according to CNN. "We have asked the Indian naval chief to investigate the matter and give a detailed report about the leak."

Stolen records include details of the stealth submarines' sensors, torpedo launch systems, and communications and navigation capabilities, CNN said.

"It appears that the source of the leak is from overseas and not in India," the Ministry said in an online statement.

The Indian Navy commissioned six Scorpene subs from French defense contractor DCNS. But the program has been slow to take off, suffering what CNN said are "years of delays." The first boat, dubbed Kalvari, is expected to enter service this year; the remaining five should be delivered by 2020.

"DCNS has been made aware of articles published in the Australian press related to the leakage of sensitive data about Indian Scorpene," the company said in a statement. "This serious matter is thoroughly investigated by the proper French national authorities for Defense Security.

"This investigation will determine the exact nature of the leaked documents, the potential damages to DCNS customers as well as the responsibilities for this leakage," the firm added.

The news was first reported by The Australian, which posted redacted versions of the leaked documents—including technical drawings and operations manuals—online. The paperwork, which features highly sensitive information, is obscured behind an online paywall, accessible only to paying subscribers.

As reported by CNN, this breach is likely to extend beyond India: Chile, Malaysia, and Brazil have ordered versions of the Scorpene, and DCNS is under contract to build 12 submarines for Australia.

This article originally appeared on PCMag.com.