Microsoft is quietly pre-loading installation components for Windows 10 onto the PCs of users who have not opted to upgrade to the new operating system.
The company late last week said the move was intended to "help customers prepare their devices for Windows 10 by downloading the files necessary for future installation".
"This results in a better upgrade experience and ensures the customer's device has the latest software. This is an industry practice that reduces time for installation and ensures device readiness," the company said in a statement.
Windows 7 or 8.1 users with Windows Update set to the default option that allows the operating system to download and install fixes automatically are affected - in such cases, Microsoft will push the Windows 10 upgrade files to the PC.
iTnews was able to confirm that the files were being loaded into a hidden directory on both a Windows 7 and 8.1 PC, without any user interaction.
But Windows users have expressed anger that the unwanted download takes up storage space and causes them to exceed their data cap. The Windows 10 upgrade can be up to 6GB in size.
"I had to travel recently, so I took a laptop with [a] clean Windows 8.1 Pro install," user 'X.25' wrote on Slashdot.
"At my destination, I purchased a SIM (they only had 1GB data packages) and put it into the 3G/wi-fi router I carry.
"When I got back [after going away for a few hours] my data package (and internet connectivity) was killed because [the] Microsoft idiots decided to start downloading Windows 10 even though I have explicitly closed/rejected all the 'offers.'"
"My in-laws live in middle of nowhere Pennsylvania .... I told them to get one of the little wireless routers from Verizon, and they easily keep under their 2Gb limit," user 'coop247' wrote.
"Last month she's calling me wondering how in the world she could have gone over her limit, and how they are going to charge her US$30 and this and that. After some investigation, turns out it was Win10 downloading."
Prior to the release of Windows 10, Microsoft had been prompting Windows 7 and 8.1 users to "reserve' their copy of the operating system. Those who took up the free offer had Windows 10 pre-loaded onto their system prior to the release date.
Microsoft launched Windows 10 to general availability in late July.