This is a part of the service if you have opted to receive automatic updates.
According to a report from the Inquirer, Microsoft has confirmed that it automatically downloads Windows 10 into upgrade-eligible Windows PCs, regardless of whether users opted-in to the free upgrade or not. Reports from such users indicate that upgrade files, ranging from 3.5 to 6GB in disk space, were downloaded and stored in the rather secluded ~BT folder, wasting both disk space and valuable, metered bandwidth. According to some of the victims, this unprovoked behavior caused their monthly bandwidth allowances to cap.
Then you will be prompted to update by those MS popups regularly.
Windows belongs in a Virtual machine under Linux IMO because there the tampering with the hardware is not such a big problem.
It is not a big problem that Microsoft offers updates, but doing it without informing you is somewhat sneaky:
The prime issue here isn’t necessarily what they did, or what they’re planning, but the lack of transparency. None of these actions were what you’d call “marketing points”, and the discoveries of these features were not announced directly by Microsoft itself in advance, but by keen users.
The biggest problem with this is that Microsoft needs to build confidence after PRISM. Marketing "trust us" takes more than money and TV time:
Still, it really begs the question: just what else is Microsoft doing with our computers behind the scenes? And at what point will they have gone too far? Or has the company crossed that line already?
Microsoft may not even have a choice in the matter as their official response to PRISM shows:
Finally when we upgrade or update products legal obligations may in some circumstances require that we maintain the ability to provide information in response to a law enforcement or national security request. There are aspects of this debate that we wish we were able to discuss more freely. That’s why we’ve argued for additional transparency that would help everyone understand and debate these important issues