True, all the above.
A 'guest' is anyone(anything) that accesses the forum without being logged-in. Well-known search engine crawlers are listed separately (Google, Yahoo!, Bing...).
'Guests' have the ability to browse/view all the topics/postings, but not to view the member lists or member map. Guests also cannot post or PM anyone.. logged-in members are the only ones allowed to post/upload attachments/send PMs.
The forum also uses several mechanisms to 1) greatly hinder spambot auto-registrations, 2) manual vetting to approve new registrations, 3) member/admin's vigilance to quickly id/eject a spammer from the forum.
(BTW.. I've moved this topic to the forum area).