Details are sketchy, but apparently a recent Windows 10 update caused major problems for some users. Affected users were suddenly unable to access the Internet. December’s Patch Tuesday (earlier this week) included an update that addresses this problem.
This issue once again raises the question of whether Microsoft can be trusted not to push flawed Windows updates, especially now that updates are essentially mandatory and unavoidable.
Update 2016Dec16: Many of the Knowledge Base pages on the Microsoft support site now include this message at the top: “If you are experiencing issues connecting to the internet we recommend you restart your PC by going to Start, clicking the Power button, then choosing Restart (not Shut down).” No further explanation is provided.