(Associated Press) – Apple released a significant security update for iPhones and iPads Thursday to patch newly discovered security vulnerabilities in the devices’ system software.

The issue was discovered by researchers at the University of Toronto’s Citizen Lab, who said the software flaw was being “actively exploited” to deliver commercial spyware called Pegasus developed and sold by the Israeli company NSO Group.

Pegasus is an expensive tool typically used to target dissidents, journalists and political opponents, so ordinary users likely have little to fear.

Still, Citizen Lab recommends that all users should immediately update their devices.