Don't forget the rumours that Eliohann is suffering from multiple personality disorder as a result of his Matrix experiences; Both the Cerberus and Neurosis posters are rumored to be Eliohann, after all.
Both Cerberus and Neurosis are confirmed to be Eliohann. His main handle is Cerberus, but he also posts as Neurosis from time to time. It is like having two Facebook accounts, one for 'public' things (or as public as a dragon e-ghost gets), and one for things you want a step removed from yourself. Doesn't mean he has multiple personalities.
And we have no idea whether e-ghosts can be affected by CFD. Since CFD spreads via nanites overwriting the meat brain, I'd have to say that it wouldn't likely affect non-biological systems. This also leads to a possible 'cure' for CFD: uploading the person's consciousness as an e-ghost before it can be overwritten.
As for Sybil being Eliohann, I don't think so. From all accounts, Eliohann's e-ghost has been afforded all the rights and privileges of dragonkind by Celedyr. No, I'd say that Sybil is likely one of the many e-ghosts NeoNET was experimenting on in Albuquerque and other places, such as the containment unit that features in the Project Imago run in Corporate Intrigue. That's just one facility, and the run took place sometime after Miles Lanier had been infected, though I haven't checked to see if it was prior to Fastjack and Riser's infections.
The fractured nature of CFD, and the fact that it competes against itself, suggests to me that there has been a shift within the 'viral code'. Whenever you copy a file, there's a chance that some information may become corrupted in the transfer. Same goes for cloud computing and other methods. This probability is low, but it is not zero. When you copy it again and again (as new nanites are added or converted), while using cloud computing models to distribute processes across the nanites in a person's body, that probability rises substantially, especially when the initial code is potentially a corrupted or Dissonance-influenced e-ghost. This easily explains the multiple strains, and so on.
So here's what we know. Pax has a technomantic ritual at her disposal to drive AIs insane, turning them into ferals or perhaps even dissonants. Celedyr has been capturing and experimenting on AIs (especially e-ghosts) perhaps since the original Project Imago. Remember, that was a Transys Neuronet project, and Transys was Celedyr's company before the merger with Erika and then Novatech. Renraku (and probably others) have been experimenting on social engineering via nanites. Any one of those could easily have sparked this off, but I agree that it was likely a combination of unintended consequences, like how a scientist is working in a lab, and accidentally discovers Teflon. Except instead of making wonderful nonstick cooking ware, you have a nanotech virus that makes a zombie apocalypse look quaint.