The home page of the CBI website had a message from the 'Pakistani Cyber Army' warning the Indian Cyber Army not to attack their websites.
The CBI website, supposed to be one of the most secure websites, is connected to the command centre of world police organisation - Interpol - 24x7.
The message from the hackers also spoke about the filtering controls provided by the National Informatics Centre (NIC), a body which mans computer servers across the country. It also claims to have hacked another 270 websites.
Intelligence agencies have been often warning the government that proper cyber security was not being ensured in government offices and that no security audit was being carried out.
The website has still not been restored. In a late night statement, the investigating agency said, "CBI is aware that its official website has been hacked and defaced. An inquiry has been launched and necessary remedial measures are underway to restore it."
Telecom Minister Kapil Sibal has said that the cyber attack on the CBI website is serious issue and that he would look into it. "These are important issues, we will look into it," Sibal said. (Watch)
Speaking on the issue, Supreme Court advocate and cyber law expert Pavan Duggal said the hacking of CBI website is an act of cyber war. "I think this is not a mere hacking incident. It is a step towards a cyber war," he said.