Despite a ban, use of pen drives has emerged as the main threat to cyber security in defence forces as it is responsible for over 70 per cent of such breaches in the three Services.

The use of pen drives as an easy-to-carry storage device has increased in the recent past and internal reports have confirmed that over 70 per cent cyber security breaches in the armed forces are due to their unauthorised use, Army officials told PTI in New Delhi.

"These pen drives, which are mostly manufactured in China, have emerged as a big threat to our cyber security systems," they said.

Fresh cyber security guidelines have been issued by the Army headquarters to protect sensitive military networks from hacker attacks, sources said.

Measures have been taken by the other two services also to tighten their cyber security as IAF also recently issued instructions to its personnel warning them against having any official data on their personal computers and pen drives.

All personnel have been asked to declare their Information Technology assets and have been asked not to have any official data on them, IAF officials said here.

Anybody found violating these instructions in checks by cyber security personnel will draw strict action which may even amount to disciplinary action including court martial, they said.

When asked about the development, IAF spokesperson Wg Cdr Gerard Galway confirmed the steps taken by the Air headquarters to safeguard its cyber assets and secret information.

Sources said generally it is found that officials use pen drive to store official data for use at their personal computers but from there, it is transmitted from their IP addresses to hackers from the 'malware' present in the pen drives.

About a couple of years ago, a Major posted in Andaman and Nicobar Islands was apprehended as it was found that sensitive data was being transferred from his computer.

However, it later emerged that his system had been hacked and spying viruses were transferring information to other computers.

An IAF Junior Warrant officer was also apprehended by officials after he was found in possession of unauthorised CDs carrying official information.

The Navy's Eastern Command was also affected after hacker groups were found to be stealing information from its computers there due to malware put in them by external drives.

As part of efforts to counter cyber attacks, the National Security Council has also been discussing designating certain intelligence agencies under the Defence Ministry for countering cyber offensives against the country.