Microsoft is issuing a rare out-of-band security update to supported versions of Windows today. The software update is part of a number of fixes that will protect against a newly-discovered processor bug in Intel, AMD, and ARM chipsets. Sources familiar with Microsoft’s plans tell The Verge that the company will issue a Windows update that will be automatically applied to Windows 10 machines at 5PM ET / 2PM PT today.

The update will also be available for older and supported versions of Windows today, but systems running operating systems like Windows 7 or Windows 8 won’t automatically be updated through Windows Update until next Tuesday. Windows 10 will be automatically updated today.

Firmware updates also required

While Microsoft is quickly addressing the issues, the fixes will also rely on firmware updates from Intel, AMD, or other vendors that are rolling out. Some anti-virus vendors will also need to update their software to work correctly with the new patches, as the changes are related to Kernel-level access.

The firmware updates and software patches could cause some systems to run slower. Sources familiar with the situation tell The Verge that Intel processors that are based on Skylake or newer architecture won’t see a significant performance degradation. However, older processors could slow down more significantly due to the firmware and software updates.

Intel says any slow downs will be “workload-dependent,” but the company has not expanded on how this will affect older machines. Microsoft is also planning to update its cloud-based servers with the latest firmware and software patches, and these updates are rolling out now.

The Verge understands that Google is planning to document and disclose the security flaws in processors at 5PM ET today. The exact bug appears to be related to the way that regular apps and programs can discover the contents of protect kernel memory areas. Kernels in operating systems have complete control over the entire system, and connect applications to the processor, memory, and other hardware inside a computer. There appears to be a flaw in modern processors that let attackers bypass kernel access protections so that regular apps can read the contents of kernel memory.

Software vendors like Microsoft and other Linux programmers are protecting against this by separating the kernel's memory away from user processes in what’s being called “Kernel Page Table Isolation.” Linux patches have been rolling out over the past month, and now Windows patches are being made available today.

Microsoft has confirmed the Windows update in a statement:

We're aware of this industry-wide issue and have been working closely with chip manufacturers to develop and test mitigations to protect our customers. We are in the process of deploying mitigations to cloud services and have also released security updates to protect Windows customers against vulnerabilities affecting supported hardware chips from Intel, ARM, and AMD. We have not received any information to indicate that these vulnerabilities had been used to attack our customers.

Update, 5:10PM ET: Article updated with Microsoft’s official statement.