Facebook sued surveillance firm NSO Group on Tuesday (October 29).
The U.S. tech giant alleges the Israeli company hacked users of its WhatsApp messaging platform earlier this year.
In a lawsuit filed in San Francisco Facebook accuses NSO of targeting journalists, diplomats, political dissidents and others.
Facebook-owned WhatsApp - also a plaintiff in the action - said in a statement that it believed the attack 'targeted at least 100 members of civil society'.
NSO denied the allegations.
Facebook wants NSO banned from accessing its services and it's also seeking other unspecified damages.
NSO allegedly used a flaw in WhatsApp to hijack phones.
WhatsApp said the attack exploited its video calling system in order to send malware to the mobile devices of a number of users.
The malware would then allow NSO clients - said to be governments and intelligence organizations - to secretly spy on a phone's owner.
WhatsApp said it believed 1,400 users were targeted.
The messaging service has 1.5 billion monthly users and has a high level of security, including end-to-end encrypted messages that cannot be deciphered by WhatsApp or other third parties.