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Many years ago I got a call from an account I used to work on. They'd had some recommendation to reduce the number of enterprise adminsistrators they had, and use one time access to the built in admin account, using some app they'd been sold. So they removed everyone's admin access, and then realised they didn't know the Admin account password to get the ball rolling. So they called, as me and a couple of colleagues had promoted the first domain controllers back in the day and asked if I knew the Directory Services Restore Mode password,... which, luckily I had ingrained in my memory (and that we had lodged somewhere safe, but our jobs were outsourced, people left offices, safes were disposed of, etc). So they had to roll back their AD to before the fudge-up.