Excerpt from a forthcoming blog post, FYI:

In Win10 x64 1903, I ran SystemPropertiesAdvanced > Advanced tab > User Profiles > Settings. At that location, I found myself in a User Profiles window, with a list of "Profiles stored on this computer." Among those profiles, I saw two "Account Unknown" entries. I was able to remove each of those by selecting and clicking Delete. But after I deleted one of them, the desktop went black. It then occurred to me that I had deleted the accounts installed by the BOINC software. Apparently the BOINC programmers had failed to attend to this detail -- to insure, that is, that their accounts would be named in the User Profiles window.

???

BOINC will only install a limited user account (named boinc_master) when you install BOINC as a service. When installed not as a service it will no longer add the limited user account or the user groups associated with the account (boinc_projects, boinc_users, boinc_admins) but as you can see, they're all named.

---