There are some peeps who, for various reasons, cannot activate Windows 10. They cannot afford to buy Windows 10, or are not eligible for a free upgrade, or don't want to or don't know how to employ dodgy methods of authentication. Would it be possible and practical for them to run Windows 10 without activating it? How does Windows 10 behave when it is not activated? I installed Windows 10 build 10240 in VirtualBox on 7/15/2015. Used an ISO that I created from an ESD file. 10240.16384.150709-1700.th1_clientpro_ret_x64fre_en-us_9d40e15f430ab89a1eabb165acbf40c9f07d18bb.esd en_windows_10_pro_10240_x64_dvd.iso Here are some things I noticed: After a day or two, Personalization changes were disabled about 1/2 hour after booting. Changes could be made within 1/2 hour of booting, but were disabled thereafter. Any changes made to Personalization would be persistent. They would not be undone. When Personalization was disabled, it could be re-enabled by rebooting. After several days, Personalization would only be enabled for a few minutes after booting, not 1/2 hour. After a few days, I noticed that when the machine had been running for 5 or 6 hours, a watermark would appear on the lower right part of the screen. It would appear not only on the Desktop, but also on any windows whose area covered the lower right part of the screen. Rebooting would cause the watermark to disappear, until 5 or 6 hours later when it would re-appear. After a few days, I noticed some Universal Apps would not work. When I tried to open them, their window would flash briefly and then disappear. The following Universal seemed to work OK: Calendar, Contact Support, Cortana, Mail, Maps, Edge, OneDrive, OneNote, Xbox. Other Universal apps did not work. That is all I have noticed so far. I wish somebody else would try this experiment and report their findings.