The forum 'who's on-line' shows that two guests are posting. But guests cannot post. However it also shows that two member's ID is being hidden. So does that mean that those two hidden members are listed as guests, while posting?
Yes users with hidden profiles are shown as guests in that list.
Thanks. I cant work out why a person posting would hide their ID because their post will be in their name. Anyway it's up to them. 'It's a free country'. Or maybe it's a police state? I'm not so sure these days.
Paranoia maybe. I do it sometimes because it's happened where I've looked at an old thread which hasn't been posted on for several months and within minutes somebody else has posted on that thread, usually it's the same person. So yes sometimes I stick myself on hide. I notice Grahame and Smiffy also hide themselves.
How do you know if they are hidden? 
Because you click on their profile and it says when they were last active, do that several times over half an hour when they have made a dozen posts then you can deduce from that, that they have opted to hide when active.
Also when there is only me and one other person online (early most mornings) and one is hidden, but posts are being made, then obviously that poster is hidden.