After installing the update users say their PCs are unable to boot and eventually get stuck in an endless loop, as they try to roll back to an earlier version of the OS.

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A Windows patch to reduce the risk from exploits for the Meltdown and Spectre CPU flaws is reportedly preventing PCs with older AMD processors from booting.

The recent update, KB4056892, seems to be causing problems for computers running on Athlon X2 processors.

Despite being older machines, the CPUs date from about the mid-to-late 2000s, users say their PCs were running Windows 10 without issue before installing the update.

After installing the update users say their PCs are unable to boot and eventually get stuck in an endless loop, as they try to roll back to an earlier version of the OS.

Some users report they were able to block the update by using the Hide/Show troubleshooter, as outlined here, but Microsoft is yet to provide official guidance for affected users.

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Windows 10 Home users have no easy way of deferring updates, and some users with affected PCs express frustration at suffering as a result of a patch primarily aimed at Intel processors.

AMD processors do not have the Meltdown design flaw, and, while they are affected by Spectre, this flaw is thought to be far harder to exploit in an attack.

Spectre and Meltdown are design flaws in modern processors that open a massive range of PCs, phones, tablets and servers to attack.

The two vulnerabilities in modern chip design could allow attackers to bypass system protections to read sensitive information, such as passwords, from memory.

The recent Microsoft patch applies to all supported versions of Windows and Windows Server, Microsoft SQL Server and the Edge and Internet Explorer 11 browsers. It's not certain that Microsoft's patches for the Meltdown and Spectre flaws caused the problems, given KB4056892 contained more than these specific security fixes.

Microsoft delayed installation of the update on some PCs, until anti-virus companies were confident it wouldn't conflict with their products. Most anti-virus vendors say their software is now compatible with the patch, and the majority of systems are expected to be eligible to receive the update by Tuesday 9th January.

A Microsoft spokeswoman said of the Meltdown/Spectre chip flaws: "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."

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