2
by Valkrist
99% of them are bots.
If you click on 'Who's Online' at the bottom of the forum page, it will typically only display whatever registered users are on at the time. However, at the very top, you will see an option to 'Display Guests'.
Click on that and it will put up a list showing the source of all these creepy crawlies. In the displayed code, you will most likely see the word 'bot', which means exactly that: automated software that just crawls along the web looking for whatever. These are typically used for information data harvesting. You will even notice a few that say they are actively replying to a topic somewhere, which is a perfect example of the infestation by non-human foreign participants that plague services like Twitter and Facebook, fulfilling whatever nefarious agenda they are on. These bots are obviously clued out as to the fact that posting while unregistered will produce 100% of nothing.
Then there are the legitimate one or two persons that are just browsing the forum from the outside, likely brought here by Google or whatever.
Hope that clears it up.