Pretty much nothing. They've always been there (they're search engine bots) but now you can see when their viewing the site. Not much point, i guess.
A bot is a computer program. There are people who write these programs that just search the internet for forums (like this one), and when the find one that is unprotected, they will post all kinds of stuff. Links to websites, porn, etc.. It looks like this forum is pretty well protected tho...