Massive security vulnerabilities in modern CPUs are forcing a redesign of the kernel software at the heart of all major operating systems. Since the issues—dubbed Meltdown and Spectre—exist in the CPU hardware itself, Windows, Linux, Android, Macs, Chromebooks, and other operating systems all need to protect against it. And worse, it appears that plugging the hole will negatively affect your PC’s performance.

Everyday home users shouldn’t panic too much, though. Just apply the latest operating system updates and keep your antivirus software vigilant, as ever.

Here’s a high-level look at what you need to know about Meltdown and Spectre, in plain language. If you want a deep-dive into the technical details, be sure to read Google’s post on the CPU vulnerabilities. We’ve updated this article repeatedly as new information becomes available.

Meltdown and Spectre CPU flaw FAQ

Editor’s note: This article was most recently updated to include many more details about the Meltdown and Spectre CPU flaws, as well as PC performance comments from Intel and AMD.

Give it to me straight—what’s the issue here?

Again, the CPU exploits in play here are extremely technical, but in a nutshell, the chip’s kernel is leaking memory because of how it handles “speculative execution,” which modern processors perform to increase performance. An attacker can exploit these CPU vulnerabilities to expose extremely sensitive data in your protected kernel memory, including passwords, cryptographic keys, personal photos, emails, or any other data on your PC.

Meltdown is the more serious exploit, and the one that operating systems are rushing to fix. It “breaks the most fundamental isolation between user applications and the operating system,” according to Google. This flaw most strongly affects Intel processors because of the aggressive way they handle speculative execution.

Spectre affects AMD and ARM processors as well as Intel CPUs, which means mobile devices are at risk. (We have a separate FAQ on how Spectre affects phones and tablets.) It’s “harder to exploit than Meltdown, but it is also harder to mitigate,” Google says. There may be no hardware solution to Spectre, which “tricks other applications into accessing arbitrary locations in their memory.” Software needs to be hardened to guard against it. 

What’s a kernel?

The kernel inside a chip is basically an invisible process that facilitates the way apps and functions work on your computer. It has complete control over your operating system. Your PC needs to switch between user mode and kernel mode thousands of times a day, making sure instructions and data flow seamlessly and instantaneously. Here’s how The Register puts it: “Think of the kernel as God sitting on a cloud, looking down on Earth. It’s there, and no normal being can see it, yet they can pray to it.”

How do I know if my PC is at risk?

Short answer: It is.