It looks like Microsoft really wants to get Windows 10 onto your system, whether you want it or not. "I know of two instances where people on metered connections went over their data cap for August because of this unwanted download. My own internet (slow DSL) was crawling for a week or so until I discovered this problem. In fact, that's what led me to it. Not only does it download, it tries to install every time the computer is booted."