On reddit,
there were numerous complaints from IT specialists and ordinary users that the Microsoft update
KB3035583 (
Update installs Get Windows 10 app in Windows 8.1 and Windows 7 SP1 ) released by Microsoft automatically updates the OS to Windows 10. Despite the fact that Microsoft disowned such behavior of the update, the number of users facing this problem has already become very large.

The update specializes in installing the GWX application (Get Windows 10) to upgrade to the new version of the OS as desired, but not automatically. Some users who were upgraded in this way also started experiencing problems with the RAID system.
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The above reddit topic will help users who have experienced this problem, as well as possible problems installing Windows 10 on a PC. As a preventive measure, users recommend not installing the released update KB3035583.

Complaints of users in the topic reddit on problems with auto-update.