Jawn beat me to it....Well...I'm not deleting this post.
Probably bots of some description...
The only reason I say so (apart from Cirn0 once saying the same) is because if you scroll down to the "who's online" and give it a click then refresh the page, it can go from 20-30 guests to just 2-3 in just a couple of seconds. Then refresh it again and wow, they are all back. "Reading" posts from years ago for 20 seconds and then leaving.
But yeah, like John said...Bots innit.