"We are Unbeatable. You...kill innocent people in Kashmir and call your self defenders of your country. You...violate the ceasefire on border and call it 'Surgical Strikes'. Now kiss the burn of Cyber War," the hackers said in the post replete with expletives.
The cyber attack was noticed around 7:15 pm.
When contacted, the office of NGT Chairperson Justice Swatanter Kumar said that he was not available for comments.
Seven terror launch pads were targeted across the LoC by special forces of the Indian army during the 'surgical strike' on September 29.
This is the second time after 2013 that the website has been hacked.
In April, 2012, the Delhi high court bar association's website was defaced by Pakistani hackers.