Through an apparent glitch that happened sometime over Sunday, the Windows Device Recovery Tool (WDRT), which is used to recover Windows 10 Mobile devices, as well as the first generation HoloLens was pulled offline, likely by accident.
Users on Twitter started to question why it was no longer possible to download or install the WDRT, and because Microsoft's firmware servers are offline, even if you have the tool, it cannot be installed because it pulls down files to complete the installation.
However, it seems that Microsoft is on the case and the appropriate people have been informed. As of writing, the tool still cannot be downloaded or used, we'll keep an eye out for an official response from Microsoft and update this article accordingly.
Update: Microsoft has confirmed that the Windows Device Recovery Tool is once again up and running.