"Government of India is concerned at the breach of privacy of citizens of India on the messaging platform WhatsApp. We have asked WhatsApp to explain the kind of breach and what it is doing to safeguard the privacy of millions of Indian citizens," tweeted Union Minister Ravi Shankar Prasad.

Nihal Singh Rathod, a human rights lawyer representing several accused in the Bhima-Koregaon case, is among the targets. Others include activist Bela Bhatia, lawyer-activist Degree Prasad Chauhan, rights activist Anand Teltumbde and journalist Sidhant Sibal.

"The person who called me explained how I had been targeted and the person clearly told me 'we can clearly and categorically say your own government has done this'," Bela Bhatia, an activist who works in Chhattisgarh, told NDTV.

The Israeli NSO, denying any wrongdoing, stated, "Our technology is not designed or licensed for use against human rights activists and journalists" and is licensed only to "vetted and legitimate government agencies".

The spyware gave snoops access to users' messages, calls and passwords as it took over the phone's operating system. It could also turn the mobile into a microphone that could listen to conversations in a room.

WhatsApp, seeking more than $75,000 in damages from NSO, said in a statement: "We quickly added new protections to our systems and issued an update to WhatsApp to help keep people safe. We are now taking additional action, based on what we have learned to date." WhatsApp has over 1.5 billion users globally, of which India accounts for about 400 million.

The spyware "Pegasus" gets into the user's phone when the person gets a video call. As the phone rings, the attacker transmits a malicious code and the spyware is installed even if the user does not answer the call at all.

By taking over the phone's systems, the attacker gets access to the user's WhatsApp messages and calls, regular voice calls, passwords, contact lists, calendar events, phone's microphone and camera.

Pegasus was designed, in part, to intercept communications sent to and from a device, including communications over iMessage, Skype, Telegram, WeChat, Facebook Messenger, WhatsApp, and others.