Refusing to divulge identities or the exact number of those targeted in India, WhatsApp said it had in May stopped a highly sophisticated cyber attack that exploited its video calling system to send malware to its users.
The mobile messaging giant said it had sent a special WhatsApp message to approximately 1,400 users that it has "reason to believe were impacted by this attack to directly inform them about what happened".
While the messaging giant didn't disclose the details or the number of people affected in India, a WhatsApp spokesperson said: "Indian users were among those contacted by us this week".
WhatsApp has over 1.5 billion users globally, of which India alone accounts for about 400 million.
Denying allegations, NSO said it provides "technology to licenced government intelligence and law enforcement agencies to help them fight terrorism and serious crime" and is not "designed or licensed for use against human rights activists and journalists."
Meanwhile, the Indian IT Ministry has written to WhatsApp, seeking a detailed response by Monday.
A senior government official told PTI that WhatsApp has been asked to give a detailed response to the entire allegations and the extent of users compromised in India.
WhatsApp had on Tuesday filed a lawsuit in a California federal court against NSO Group, which allegedly developed the spyware, saying an attempt was made to infect approximately 1,400 "target devices" globally, including some in India, with malicious software to steal valuable information from those using the messaging app.
WhatsApp said it "believes the attack targeted at least 100 members of civil society... this number may grow higher as more victims come forward".
WhatsApp Head Will Cathcart said these victims include human rights defenders, journalists and other members of the civil society across the world.
"Tools that enable surveillance into our private lives are being abused, and the proliferation of this technology into the hands of irresponsible companies and governments puts us all at risk," Cathcart said in an op-ed in The Washington Post.
Cathcart asserted that WhatsApp was committed to the fundamental right to privacy and that it is working to stay ahead of those who seek to violate that right.
A cybersecurity research lab at the University of Toronto, Citizen Lab, had helped WhatsApp investigate the hacking incident.
In response, NSO said: "In the strongest possible terms, we dispute today's allegations and will vigorously fight them. The sole purpose of NSO is to provide technology to licenced government intelligence and law enforcement agencies to help them fight terrorism and serious crime. Our technology is not designed or licensed for use against human rights activists and journalists. It has helped to save thousands of lives over recent years."
"The truth is that strongly encrypted platforms are often used by pedophile rings, drug kingpins and terrorists to shield their criminal activity. Without sophisticated technologies, law enforcement agencies meant to keep us all safe face insurmountable hurdles. NSO's technologies provide proportionate, lawful solutions to this issue," it said.
NSO said any use of the product other than to prevent serious crime and terrorism was a misuse.
"We take action if we detect any misuse. This technology is rooted in the protection of human rights - including the right to life, security, and bodily integrity - and that's why we have sought alignment with the UN Guiding Principles on Business and Human Rights, to make sure our products are respecting all fundamental human rights," it said.
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