The bots you see here are the 'spiders' that search engines like Yahoo, MSN and Google use to index websites. They go around the internet checking websites out so they can give better results when a user looks up a keyword, such as 'anime' or 'roleplay'. These kinds of bots are okay, and are actually beneficial.
The bots you initially thought of are probably 'spambots', those automated programs that start posting ads and stuff. Thankfully, this site currently uses an admin-approval system for new members. That means, no one can post unregistered, so we shouldn't have any problems with random 'guest users' posting up spam and whatnot.