Apple and Google have sent a new round of cyber threat notifications to users around the world, the companies said this week, announcing their latest effort to insulate customers against surveillance threats.

Apple and the Alphabet-owned Google are two of several tech companies that regularly issue warnings to users when they determine they may have been targeted by state-backed hackers.

Apple said the warnings were issued on Dec. 2 but gave few further details about the alleged hacking activity and did not address questions about the number of users targeted or say who was thought to be conducting the surveillance. Apple said that “to date we have notified users in over 150 countries in total.”

Apple’s statement follows Google’s Dec. 3 announcement that it was warning all known users targeted using Intellexa spyware, which it said spanned “several hundred accounts across various countries, including Pakistan, Kazakhstan, Angola, Egypt, Uzbekistan, Saudi Arabia, and Tajikistan.”

Google said in its announcement that Intellexa, a cyber intelligence company sanctioned by the U.S. government, was “evading restrictions and thriving.” Executives tied to Intellexa did not immediately return messages.

Previous waves of warnings have triggered headlines and prompted investigations by government bodies, including the European Union, whose senior officials have previously been targeted using spyware.

Threat notifications impose costs on cyber spies by alerting victims, said John Scott-Railton, a researcher with the Canadian digital watchdog group Citizen Lab. He said they were “also often the first step in a string of investigations and discoveries that can lead to real accountability around spyware abuses.”