The most widely used anti-bot technique is the use of CAPTCHA, which is a form of Turing test used to distinguish between a human user and a less-sophisticated AI-powered bot, by the use of graphically-encoded human-readable text. Examples of providers include Recaptcha, and commercial companies such as Minteye, Solve Media, and NuCaptcha. Captchas, however, are not foolproof in preventing bots as they can often be circumvented by computer character recognition, security holes, and even by outsourcing captcha solving to cheap laborers.
Messenger Bots are created using the new Messenger API that allows a bot to send and receive messages. The Messenger Bots are essentially chat bots that you can talk to from the Messenger app. The conversations will of course be different than those you have with your Facebook friends. These bots are meant to help you get information for example you can ask the CNN bot to tell you give you the current headline news and it will fetch them for you.