The lawsuit was filed Tuesday in a federal court in California against the Israeli electronic surveillance company NSO Group. The lawsuit accuses NSO of computer fraud, breaching WhatsApp’s computer systems, and “wrongfully trespassing” on Facebook property, the Israeli business daily Globes reported.

NSO has denied that it had a role in the cyberattack, WhatsApp head Will Cathcart told the AFP news agency. He said the lawsuit was filed after an investigation showed the firm was involved.

The complaint said the attackers “reverse-engineered the WhatsApp app and developed a program to enable them to emulate legitimate WhatsApp network traffic in order to transmit malicious code” to take over devices using the Android, iOS, and BlackBerry operating systems.

The lawsuit asks the court to order NSO Group to stop these attacks and asks for unspecified damages.

NSO was targeting  the cellphones and other electronic devices of attorneys, journalists, human rights activists, political dissidents, diplomats, and other senior foreign government officials, according to the complaint.

WhatsApp in May called on users to upgrade the application to fix a security hole that allowed the upload of sophisticated malware that could be used for spying.