If you've got an Oculus Rift and you've tried to use it in the last 24 hours, you probably ran into some trouble. Early yesterday morning, folks on Reddit reported an inability to launch the Rift software. Five hours after the trouble started, Oculus made a post in its own forums acknowledging and apologizing for the problem, although it still wasn't completely clear at that point what the issue was.
As it turns out, a digital certificate required by Windows for Oculus' software had expired. The issue meant that practically all day yesterday, every single Rift kit worldwide was essentially a very expensive and awkward-to-use paperweight. Folks figured out various workarounds like simply changing the system date to before the issue started, or using NirSoft RunAsDate to make the Oculus Home app think it was running at an earlier date. Reddit poster TrefoilHat has the explain-it-like-I'm-5 version of the problem here.
Fortunately, there's no need to faff about with hacky workarounds any longer, because Oculus has now issued an official fix for the problem. Unfortunately, the certificate issue also prevents the Oculus software from simply updating itself. If you've got a Rift and want to get up and running again, you need to grab the update from Oculus directly or click here for more details on how to get set up again.