There is a debating technique that is called "reductio ad absurdum" which demonstrates the validity of a statement by proving that the opposite is impossible (absurd). A common example is "rocks have weight, or else we should see them floating in the air". Without going into technical details, I state that Microsoft are not spying on your hard disk, because if they would do so
- They have nothing to gain from the act itself.
- There is no way they could prevent destroying themselves in the process - and they know that.
Let's just assume, for the sake of argument, that Microsoft are indeed the bunch of evil scientist some people seem to think they are. Spying on you would require some data gathering process and some process of transmitting data to Microsoft, using your own network connection. Agreed?
Well then, with Windows 10 running on 75 million (and counting) machines, a substantial number of those owned by clever d- I mean smart persons - who know very well how to operate network analyzing tools like WireShark, there is no way in Hades they could keep the data transmitting part of that process secret forever. Any spying tool included in Windows 10 will be found. Sooner or later. By those smart people. By anti virus software makers. Or it will be revealed by a whistleblower. Whatever. When - not if - such a spying tool would be discovered, Microsoft would receive crackdowns from both the USA and EU governments that would make their experiences with the DOJ in the bad old days seem like a walk in the park on a sunny day, and they would loose the trust of all their clients overnight. People would stop using Windows. And what, exactly, would Microsoft have to gain? Your local games score is not that interesting, neither is your local document store. A local store of illegal imagery, music or movies may be of interest to the law, but not to Microsoft - whatever's on your PC is your responsibility.
The only 'spying' that is going on is some telemetry on apps or parts of Windows that run into trouble and report whatever happened when things went South back to Microsoft (or the app developer) to make it easier to fix those bugs. If you opt in for customer improvement programs (and I almost always do) some usage patterns may be transmitted. This is not new, telemetry has been part of the last couple of Windows releases and this is all anonymously, for the same reason - should Microsoft ever be caught red-handed spying on individual users, they would receive hell from all directions, and rightly so.
So why would Microsoft spy on your hard drive? There is nothing to gain, and everything to loose. Microsoft are in the business of making great software and services and making money with that - preferably lots, and they are pretty good and successful at that. They are not into spying, because they won't make money from the act itself but they would put nearly all of their existing money makers in very real danger. It would be just absurd to do that. It would not even make sense even when they were indeed an 'evil spying company', which they are not. They are making billions in cloud services, a business primarily based on technical excellence, high availability and above all trust. To put it very bluntly, whatever is on your hard drive cannot possibly be worth violating that trust. I am sorry to have to put it like that, but that is the simple truth.