The latest Windows patch is breaking even more PCs with antivirus installed

Now McAfee users are reporting issues, too.

3 patch training update software band aid laptop with virus binary
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The last major Windows update broke some systems with particular antivirus software installed, and it’s seemingly getting worse.

Earlier this week we reported that Microsoft halted updates to Windows PCs running Sophos and Avast’s security solutions, following user complaints that their machines were locking up or failing to boot. Since then, the list of known issues for the rogue update was itself updated to acknowledge compatibility issues with Avira and ArcaBit antivirus installed, with Microsoft temporarily blocking updates to those affected systems, too. Today, Ars Technica noticed that Microsoft is investigating compatibility issues for systems with McAfee antivirus installed, though it hasn’t started blocking the April 9 update from those PCs just yet.

Windows 7 and 8.1 computers can fall prey to the bug, along with some Windows Server installations. Windows 10 PCs don’t appear to be affected.

Affected computers either freeze outright or start acting abominably slow when you attempt to log into Windows. You can skirt the issue by booting into Safe Mode, disabling your antivirus, and rebooting your system normally.

If you need to do that, get your PC’s guard back up by activating Windows Defender in Windows 8.1, or downloading Microsoft Security Essentials for Windows 7. Both provide free real-time security for your computer. Alternatively, you could buy an antivirus solution from an unaffected vendor. 

Some of the affected antivirus vendors have already posted workarounds or updates for the problem. Microsoft’s issue tracker for the borked update includes links to the support pages created by AV vendors about this issue.

As Ars Technica notes, the support pages from Avast and McAfee hint that the problem stems from changes made to the way Windows handles its Client Server Runtime Subsystem (CSRSS). Microsoft’s tinkering with core system components have recently caused other headaches with software that sinks deep hooks into your operating system. Windows Insider preview builds for the next major Windows 10 update, releasing in late May, suffered from “Green Screens of Death” if you ran a game with built-in anti-cheat software. Microsoft has been working with anti-cheat software vendors like BattlEye to correct the issue before the May 2019 Update’s final release.

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