Unified Extensible Firmware Interface
In August 2016 it was reported that two security researchers had found the "golden key" security key Microsoft uses in signing operating systems. Technically, no key was exposed. However, an exploitable binary signed by the key was exposed. This allows any software to run as though it was genuinely signed by Microsoft and exposes the possibility of rootkit and bootkit attacks. This also makes patching the problem impossible, since any patch can be replaced (downgraded) by the (signed) exploitable binary. Microsoft responded in a statement that the vulnerability only exists in ARM architecture and Windows RT devices, and has released two patches; however, the patches do not (and cannot) remove the vulnerability, which would require key replacements in end user firmware to fix.