It can get annoying sometimes when you own a forum because of all the bots and sometimes people spamming your site with useless content or advertisements. The bots used by spammers are getting a lot more intelligent and that means that some anti-spam methods just don't work anymore. I've however noticed that, personally, custom questions work best to stop bots. For some reason, questions like "What colour is a banana?" seem to be impossible for bots to answer. What anti-spam methods work best for you?