Microsoft is downloading Windows 10 to Windows 7 and 8 machines, even if the user hasn’t expressed permission. A reader of The Inquirer saw that the ~BT Windows 10 folder had appeared on his system even though he hadn’t reserved a copy. He only noticed after spotting a number of failed ‘Upgrade to Windows 10’ messages in his Windows Update history. Microsoft has confirmed this is happening to The Inquirer, as well as VentureBeat and PCWorld when reached for a statement.
Users have been able to opt-in to the free Windows 10 upgrade if they're running Windows 7 or 8, but apparently even if they don't, the files are being downloaded anyway. It's happening on devices which have automatic updates allowed, which we'd generally recommend to catch the latest security and stability updates for Windows.
When asked about this issue, Microsoft responded by saying “For individuals who have chosen to receive automatic updates through Windows Update, we help upgradable devices get ready for Windows 10 by downloading the files they’ll need if they decide to upgrade. When the upgrade is ready, the customer will be prompted to install Windows 10 on the device.” Convenient, if you're installing Windows 7 or 8 specifically to upgrade to Windows 10. Otherwise, not so much.
The automatic download takes up between 3.5 and 6GB of storage space, which may not sound like a lot, but it’s not an insignificant amount for some users. Windows tablets with smaller hard drives are affected, and people with data caps on their Internet connections certainly don’t want that amount of data coming in without permission. The background download could affect people with poor Internet connections too, without them being aware that they're downloading unnecessary files.
Since launch, over 75 million devices have made the upgrade to Windows 10, and some sources say that the number is closer to 100 million.