Another day, another controversy about Microsoft's automatic updating policies. This time it seems that Microsoft is secretly downloading Windows 10 installation files onto the devices of Windows 7 and 8.1 users.

Microsoft does have a service where users can sign up to reserve their free upgrade to Windows 10 and be notified when their PC is ready to make the jump. The problem is that users who have not opted to reserve an upgrade are discovering installation files in their devices.

The scoop comes courtesy of The Inquirer. The website received a tip from a reader saying that he noticed a ~BT folder containing the files.

"The symptoms are repeated failed 'Upgrade to Windows 10' in the WU update history and a huge 3.5GB to 6GB hidden folder labelled '$Windows.~BT'." Said the reader.

Microsoft told The Inquirer that the Windows 10 files come in the form of an automatic update, so any user that has chosen to have uploads download automatically may see the Windows 10 install on their hard drive.

"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."

The automatic update feature is usually used to roll out small software updates like patches and security fixes. A Windows 10 install weighing in at 3-6GB seems a like a lot of data to be forced on users without their knowledge.

Many irate users on social networking sites like reddit have complained about the download, saying it has caused them to go over the monthly data caps set by internet service providers.