The files needed to install Windows 10 are being automatically downloaded to Windows 7 and 8.1 users by Windows Update — even if users have no intention of upgrading.
According to The Register, the upgrade files are being downloaded even by users who have not opted to digitally "reserve" a copy of Windows 10 in Microsoft's app.
It sounds like it could be a useful move to make updates easier for people who haven't made the jump yet, but it could also be problematic. Unlike regular Windows Update files, the Windows 10 update is obviously rather large — somewhere in the region of 3GB, which not everyone will have free. Worse still, if a user is on a metered connection and can only download a limited amount of data, then the update could secretly screw up their bandwidth allowance.
Microsoft confirmed the news to The Register, saying that "For those who have chosen to receive automatic updates through Windows Update, we help customers prepare their devices for Windows 10 by downloading the files necessary for future installation."
The good news for those who don't want Windows 10 is that apparently the bulky file can be removed in Microsoft's Disk Cleanup Utility... But perhaps it could also be a good excuse to finally get around to upgrading?