Apple said it is suing NSO after the company's software, called Pegasus, was used to attack a small number of its customers worldwide.

In a complaint filed in court in California yesterday, it said NSO employees 'have created highly sophisticated cyber-surveillance machinery that invites routine and flagrant abuse'.    

The suit from the Silicon Valley giant adds to the trouble facing embattled NSO, which was engulfed in controversy over reports that tens of thousands of activists, journalists and politicians were listed as potential targets of its Pegasus spyware. 

US authorities just weeks ago blacklisted NSO to restrict exports from American groups over allegations the Israel firm 'enabled foreign governments to conduct transnational repression.'