I had already installed the UEFI USB image. i got multiple virus warnings d/ling the universal USB image.

Got a bit freaked by that, trashed the usb stick, but it changes the partitions on you and LOCKS them. turned a nice sandisk 64GB into a 126 Mb stick.

computer management would not fix it.

I ended up going oldschool with diskpart, and good old delete part override cleared up the shenanigans.

USE AT YOUR RISK.

at the very least, run whatever .7z you choose through virustotal.