My records agree with Tim's. I noticed that entry a week or so ago, and thought it looked strange. It looked like either a glitch in a Merge run and/or an attempt to enter <private> profiles in a way I've not encountered before. I suspect BOTH.
I hope I have not trodden upon somebody else's toes here, but I have deleted the parental relationship to William Robert Rea & Estelle McClure, which disconnected "Hidden" & descendants from the Tree without destroying the relationships within the "hidden" family, which seems to be also linked to somebody else's data. No ownership of this line is indicated, as far as I can tell.
In the event that this was entered attempting to indicate that there is an otherwise unidentified illegitimate child that exists, I hope that whoever entered that relationship lets us know and perhaps with curator help, we can find a way to enter that info in a way that won't confuse the GENI software.
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I know some - not sure if all - of the profiles listed as "Hidden" LastName are from when Geni added all the info/profiles/trees from Y-Search.
Personally, think it was a major waste of manpower on a project that should not have been done - but a) that is hindsight and b) just because I haven't seen any pluses to it, and have seen minuses - it is still possible there are major pluses to it (if so, anyone want to give a shout out about them)
Not sure if you really meant profiles 'named' HIDDEN - which are ones Geni created from YSearch and Mitosearch -- or if you just meant Private Profiles - but if the former -- this might be of interest: https://www.geni.com/discussions/185502?msg=1240398 -- with regard to profiles from "YSearch.org or Mitosearch.org, it turns out Family Tree DNA has shut down those web sites. This makes these "HIDDEN Lastname" matches pretty useless, so we'll be removing them from Geni."