You had search engines replying to a thread?

I do realize they can't actually reply to a thread, but, yes, they were using that function, among other things. They were also using the function of replying to polls, sending messages, sending contact emails, etc. Even though there were error messages, they kept getting stuck on these types of functions for many minutes at a time, until I realized I could restrict the functions through a robots.txt file (courtesy of vbulletin.com). Of course, they do otherwise have free reign. :)

Can you use the spider.xml to block bots too if you don't have an htaccess file?