Google "indexes" the site regularly. A google bot visits and indexes all of the links and posts on this site, so that when people search for something like "ATX Community" (or any other relevant information found on this site) it'll show up in the search results.
The forum knows what this indexing bot looks like, and shows it as an active member while it's crawling the pages. It does the same for Yahoo and some other search engines.
As far as privacy goes, if you would rather people not see what posts you're reading or what area of the site you're on, you can log in anonymously. Your name will still be attached to your posts, but your movements around the site will not linked directly to you.
To log in anonymously:
1. Log out
2. Go here: http://www.atxcommunity.com/index.php?act=Login&CODE=00
3. Enter your username and password, and put a check in the box next to "Log in as invisible"
Sorry about the slow response, I'm in the process of moving. Ugh.