https://support.microsoft.com/en-us/kb/3080351
Subkey: HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate
DWORD value: DisableOSUpgrade = 1
The MSFT decision to perform forced updates is covered, for example, by Extreme Tech, February 2:"Look out: Microsoft shifts Windows 10 to ‘Recommended’ update, automatic download"
http://www.extremetech.com/computing/222326-look-out-microso...
I still believe they shouldn't have done that and I hope they get sued, heavily. Even if nobody dies, it's not OK. People had fully working computer and some of them wont. I have one such computer, which works on Windows 7 but doesn't on Windows 10.