It downloads all the ISOs from the official Microsoft servers for every recent version. For older versions like Win7/Vista/XP it is impossible to download them

It downloads all the ISOs from the official Microsoft servers for every recent version. For older versions like Win7/Vista/XP it is impossible to download them from Microsoft, because they are not available anymore on their servers. So for those I had to use an alternative mirror (BobPony), but I checked all the SHA256 checksums to make sure they are unmodified retail versions. If someone does not trust it, they can check the checksums of the downloaded ISO themselves or just dont use this container for anything below Windows 8.1.