Sophos antivirus manufacturers and Avast warn users that installing a recent Windows update may result in their computer crashing or failing to boot them.
In the notices posted on Monday, Avast said that older machines running Windows 7 or Windows 8.1 were locked or frozen at startup after applying certain Microsoft Windows updates: KB4493472, KB4493448, KB4493467, and KB4493446. Sophos has also identified the same patches at the root of some computers failing to boot when they run their own software. Sophos has also identified patches specific to Windows Server.
Windows 10 users do not seem affected, according to the information provided by both companies.
According to Sophos, Microsoft has already started to block Windows machines on which Sophos Endpoint is installed. For his part, Avast said that he was working on a fix: "We have developed micro-updates that should solve the problem and restore functionality for our users," said the company.
Avast said the micro-updates should automatically take effect. Users will be required to leave their computer for approximately 15 minutes, during which updates will take effect. If that does not work, Avast recommends restarting the machine in safe mode and then depositing a ticket with customer support. Sophos users must follow a more complicated process, including manual recovery of the machine.
The Microsoft patches in question correct a number of fixes, including Specter Variant 2 and Meltdown patches for little used Via processors, as well as authentication issues for Internet Explorer 11.
What does this mean for you? If you are a Sophos or Avast user, approach your next Windows upgrade with caution. To be honest, although the file deletion fiasco of the October 2018 update is still in our memories, most of the Windows 10 upgrades are running reasonably smoothly. Microsoft is also working on some of the worst problems and giving users more control over when and how updates happen.