Apple has said that all iPhones, iPads and Mac computers are affected by two major flaws in computer chips.
It emerged this week that tech companies have been racing to fix the Meltdown and Spectre bugs, that could allow hackers to steal data.
Apple said it had already released some patches but there was no evidence that the vulnerability had been exploited.
But it advised only downloading software from trusted sources to avoid “malicious” apps.
Mac users have often believed that their devices and operating systems are less vulnerable to security issues than, for example Android phones or computers running Microsoft systems.