In a major penetration of security, around 50 computers of the armed forces and the Defence Research & Development Organisation (DRDO) were hacked last December, and classified files could have been compromised, it emerged on Thursday.
Apparently in view of the development, an advisory has been issued to the Services that computers with internet access should be kept at a distance from those on which classified work is conducted.
A high-level probe was ordered after the security breach was detected by the intelligence agencies, PTI reported citing government sources.
The computers that were hacked are located in the South Block and belong mainly to the Army and also to the other two forces and the DRDO, they said.
The security establishment fears that up to 30 files marked as classified could have been compromised in the process.
National Security Advisor Shivshankar Menon sought to downplay the hacking incident saying there are "various forms of compromise" and "not every leaked password is a big threat to security''.
"The mere fact that some computer is open in North Block and South Block and is accessible does not mean that therefore there is big gap in security," he said.
Insisting that "things are not in bad shape", he said, "We will deal with those computers which we feel are compromised."
An advisory issued to the Services said that it was found that a spyware was detected which could read the files of computers even if they were not connected to internet, the sources said.
Armed forces have suffered a lot due to the attempts of hacking by Chinese and Pakistanis, and at least one major posted in the Andaman and Nicobar Islands has reported leak of critical information from his computer.