From Monday this week Windows 10 will automatically begin installing on many home machines running Windows 7 and 8.1.
Windows users will be able to stop the installation, as they will need to confirm they want the free upgrade to Windows 10 to continue.
But while it can be refused, the upgrade may repeatedly try to install itself on Windows 7 and 8.1 machines.
This marks the start of a new phase in the rollout of Windows 10: Microsoft has changed the status of the upgrade to that of a "recommended" update, which consumer Windows 7 and 8.1 machines typically attempt to install automatically on a regular basis.
When asked whether a Windows 7 and 8.1 machine will attempt to begin the install again after it's been declined, a Microsoft spokesman did not answer the question directly - stating only that users will be able to stop Windows 10 from installing by changing their Windows Update settings.
To stop the automatic upgrade from initiating, Windows Update settings will need to be changed from "Install updates automatically" to one of several options that allow users to choose which updates are downloaded and installed - as outlined here. Unticking the box marked "Give me recommended updates the same way I receive important updates" on the Windows Update settings page may also work.
If users do upgrade but don't like Windows 10 they will have 31 days to roll back to their previous OS.
Microsoft has previously not answered the question of whether the Windows 10 upgrade will repeatedly attempt to install on affected Windows 7 and 8.1 machines. When asked the same question last year, Jeremy Korst, general manager of the Windows and Devices team at Microsoft, said only that "the customer will have the ability to delay it for some period".
The Windows 10 upgrade is automatically being installed on many Windows 7 and 8.1 machines as a result of Microsoft changing the status of the upgrade to that of a "recommended" update.
Windows 7 and 8.1 machines sold to home users are generally configured to automatically install these "recommended" updates. Machines that have Automatic Updates turned on and the "Give me recommended updates the same way I receive important updates" option selected - Microsoft's recommended configuration when installing Windows 7 and 8.1 - will see the Windows 10 Upgrade begin to automatically install. The upgrade will be pushed to these machines as part of a phased rollout. The minority of computers that don't meet the relatively modest system requirements for Windows 10 will not receive the upgrade.
Enterprise IT administrators can disable the upgrade using Group Policy settings or by using the DisableUpgrade registry key. Microsoft advises that workarounds that rely on altering other registry keys are not "supported mechanisms" for controlling the upgrade process and are not recommended.
User numbers for Windows 10 are growing and earlier this year Microsoft announced that more than 200 million devices worldwide were running Windows 10. Among businesses, Terry Myerson, VP of Microsoft's Windows and Devices Group, said that more than 76 percent of enterprise customers were in "active pilots" and there were more than 22 million devices running Windows 10 across enterprise and education customers.
Nick Heath is chief reporter for TechRepublic. He writes about the technology that IT decision makers need to know about, and the latest happenings in the European tech scene.