The IIS_WPG user is an IIS Worker Process workgroup and is required so that IIS can start / access files in a folder
IIS_IUSRS is an Internet guest account that is used to allow anonymous access to a folder / files. This is necessary if you want the general public to be able to view something in folders, for example. website.
They are not part of the Authenticated Users group and usually require separate access to access.
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