The Indian Navy is investigating a computer hacking attack on its Eastern Naval Command, which may have stolen secret plans concerning military operations.

The command is responsible for overseeing India’s eastern border, security including the protection of strategic and commercial assets, as well as trials of the country’s first nuclear missile submarine, INS Arihant, and operations in the South China Sea.

Confirming the attack, a spokesman told the BBC that computer networks in and around the headquarters of the Eastern Naval Command were found to be infected with the thumb malware through USB drives.

“Finding the ‘smoking gun’ evidence of who was behind a particular internet attack is often very hard.”

A source familiar with the investigation also revealed to the Indian Express that the malware-infected documents remained hidden on a secret folder on the USB and when the drive was connected to an internet-enabled PC, the documents were transferred to certain IP addresses tracing to China.

According to the news agency, the hackers have used Chinese IP addresses but the final destination of the stolen documents could not be proven.

Sophos senior technology consultant Graham Cluley said thay even if a hack was traced back to a Chinese IP address, it does not necessarily mean that Chinese hackers were behind the hack.

"Finding the ‘smoking gun’ evidence of who was behind a particular internet attack is often very hard," Cluley added.

The extent of the compromised data is yet to be determined, while officials said that it was ‘premature at this stage’ to comment on the sensitivity.

A board of inquiry has been completed, which is reported to have indicted six mid-level officers in the Eastern Command over the security breach.