Okay, as for the clue....
A hidden member of another. He certainly seems to be talking about a second identity of an existing member. How many of those do we have? The only one I can think of is Frank_the_Hippo, who is actually SoP. Right?
That would be odd though, as "Hippo" isn't registered here....
Hmm. There's also USF, of course, who took control of SoP's account.
Any other thoughts? I suspect SoP based on the surface evidence, though would that require actually protecting SoP himself, or "Hippo"? My brain hurts.
EDIT: Or there is, of course, Incog himself. Wouldn't that be something...force us to discover his identity and protect him before he kills...himself?!

Yes, very unlikely, but a fun thought.