Indian government officials have confirmed that the website of the Central Bureau of Investigation (CBI) was downed late last week.
The hackers, calling themselves the "Pakistani Cyber Army", said the attack was in revenge for similar Indian attacks on Pakistani sites, local reports said.
The border dispute between India and Pakistan over Kashmir has often moved online, with both sides attempting to hack each other's sites.
Roger Rawlinson, managing director of Assurance Division at NCC Group, said the attack highlights the importance and difficulty that governments face in keeping their digital assets secure, especially when they are susceptible to attack from potentially hostile neighbors.
"While these attacks are to humiliate rather than cause damage, a more serious attack, that denies a nation of electricity, communications and financial services, would have serious implications for its economy. The exploitation of vulnerabilities in central infrastructure is increasingly being considered during conflicts," he said.
This story was first published by Computer Weekly