The Facebook-owned messaging platform said that targets included diplomats, political dissidents, journalists and senior government officials.

In a lawsuit filed in a San Francisco court, it alleged that the hacking spree occurred in 20 countries although only Mexico, the United Arab Emirates and Bahrain were identified.

NSO has denied the allegations, saying it will “vigorously fight them”. It added: “the sole purpose of NSO is to provide technology to licensed government intelligence and law enforcement agencies to help them fight terrorism and serious crime.”

WhatsApp is the world’s most popular communications software, with about 1.5 billion users in 180 countries.

The lawsuit alleges that malicious code from NSO was sent from 29 April to 10  May over WhatsApp servers. It exploited its video calling system in order to send malware to the mobile devices of users. The malware would allow NSO’s clients – said to be governments and intelligence organisations – to secretly spy on a phone’s owner, opening their digital lives up to official scrutiny. Smartphones could apparently be compromised through missed calls alone.

Facebook said NSO violated laws including the US Computer Fraud and Abuse Act.

The firm has been widely condemned for selling surveillance tools to repressive governments. It issued a statement in which it did not directly deny hacking WhatsApp but said it disputed the allegations and vowed to “vigorously fight them”.

“The sole purpose of NSO is to provide technology to licensed government intelligence and law enforcement agencies to help them fight terrorism and serious crime,” the company said.

“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.”

It said strongly encrypted platforms are used by paedophile rings, drug traffickers and terrorists and that NSO’s technologies “provide proportionate, lawful solutions”.

Facebook demands in the suit that NSO Group be denied access to Facebook’s services and systems and seeks unspecified damages.

“This is huge. I am really glad to see a tech company put their massive litigation team on the field on behalf of users,” tweeted Alex Stamos, a Stanford University researcher and former Facebook chief security officer.

Earlier this month Britain’s home secretary Priti Patel appealed to Facebook founder Mark Zuckerberg not to introduce encryption to its Messenger platform as it would hamper law enforcement operations. 

The Facebook-owned messaging platform said that targets included diplomats, political dissidents, journalists and senior government officials.

In a lawsuit filed in a San Francisco court, it alleged that the hacking spree occurred in 20 countries although only Mexico, the United Arab Emirates and Bahrain were identified.

NSO has denied the allegations, saying it will “vigorously fight them”. It added: “the sole purpose of NSO is to provide technology to licensed government intelligence and law enforcement agencies to help them fight terrorism and serious crime.”

WhatsApp is the world’s most popular communications software, with about 1.5 billion users in 180 countries.

The lawsuit alleges that malicious code from NSO was sent from 29 April to 10  May over WhatsApp servers. It exploited its video calling system in order to send malware to the mobile devices of users. The malware would allow NSO’s clients – said to be governments and intelligence organisations – to secretly spy on a phone’s owner, opening their digital lives up to official scrutiny. Smartphones could apparently be compromised through missed calls alone.

Facebook said NSO violated laws including the US Computer Fraud and Abuse Act.

The firm has been widely condemned for selling surveillance tools to repressive governments. It issued a statement in which it did not directly deny hacking WhatsApp but said it disputed the allegations and vowed to “vigorously fight them”.

“The sole purpose of NSO is to provide technology to licensed government intelligence and law enforcement agencies to help them fight terrorism and serious crime,” the company said.

“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.”

It said strongly encrypted platforms are used by paedophile rings, drug traffickers and terrorists and that NSO’s technologies “provide proportionate, lawful solutions”.

Facebook demands in the suit that NSO Group be denied access to Facebook’s services and systems and seeks unspecified damages.

“This is huge. I am really glad to see a tech company put their massive litigation team on the field on behalf of users,” tweeted Alex Stamos, a Stanford University researcher and former Facebook chief security officer.

Earlier this month Britain’s home secretary Priti Patel appealed to Facebook founder Mark Zuckerberg not to introduce encryption to its Messenger platform as it would hamper law enforcement operations.