Apple has warned owners of its iPhones, iPads and computers that they are affected by a processor flaw that could leave them vulnerable to hackers.
The US tech giant urged its millions of customers to only download software from trusted sources after the security vulnerabilities, known as Meltdown and Spectre, were revealed on Wednesday.
There is no evidence that the flaws - which affect computer processors built by Intel and ARM - have so far been exploited by hackers, although companies including Microsoft have been working to provide urgent fixes.
In a blog post, Apple said it had released software updates for iOS, the software on its phones and tablets, macOS, which is used by its computers and tvOS for its television products.
"Security researchers have recently uncovered security issues known by two names, Meltdown and Spectre," it added.
"These issues apply to all modern processors and affect nearly all computing devices and operating systems. All Mac systems and iOS devices are affected, but there are no known exploits impacting customers at this time.
"Since exploiting many of these issues requires a malicious app to be loaded on your Mac or iOS device, we recommend downloading software only from trusted sources such as the App Store."
The firm said the Apple Watch is not affected by Meltdown and it plans to release and update for its web browser, Safari, in the coming days to help defend against Spectre.
The flaws were discovered by researchers at Google and academic institutions last year, although they were kept secret.