The company issued an update for the "Meltdown" vulnerability last week, but you still need to update again to the latest iOS to avoid the numerous security gaps that affect every modern computer and smartphone chip.
Users with eligible devices should find the update in their phone's settings under General, then Software Update. The latest Apple update, iOS 11.2.2, is now available for the iPhone 5S and later and iPad Air and later.
The vulnerabilities could allow a hacker to steal information stored in the memory of a wide range of computer chips running on personal devices. That applies not just to computers and phones, but also the servers in data centers, including those used to run cloud computing services.