what happends when you get this message on a blog""( Bad Behavior has blocked 81 access attempts in the last 7 days. ) is true here
Usually a blog software name is helpful, but most likely it was blocking a site scrapper or some sort of negative useragent accessing your blog.
Just as ssandecki said, it's blocking spam and scripts with fake useragents etc. Here's the Bad Behavior site and info: http://www.bad-behavior.ioerror.us/ Seeing it has blocked 81 attempts is a good thing, it means it's working and doing it's job.