A malicious use of bots is the coordination and operation of an automated attack on networked computers, such as a denial-of-service attack by a botnet. Internet bots can also be used to commit click fraud and more recently have seen usage around MMORPG games as computer game bots.[citation needed] A spambot is an internet bot that attempts to spam large amounts of content on the Internet, usually adding advertising links. More than 94.2% of websites have experienced a bot attack.[2]

In one particularly striking example of how this rather limited bot has made a major impact, U-Report sent a poll to users in Liberia about whether teachers were coercing students into sex in exchange for better grades. Approximately 86% of the 13,000 Liberian children U-Report polled responded that their teachers were engaged in this despicable practice, which resulted in a collaborative project between UNICEF and Liberia’s Minister of Education to put an end to it.
This is where most applications of NLP struggle, and not just chatbots. Any system or application that relies upon a machine’s ability to parse human speech is likely to struggle with the complexities inherent in elements of speech such as metaphors and similes. Despite these considerable limitations, chatbots are becoming increasingly sophisticated, responsive, and more “natural.”
2a : a computer program that performs automatic repetitive tasks : agent sense 5 Several shopping "bots" will track down prices for on-line merchandise from a variety of vendors.— Sam Vincent Meddis especially : one designed to perform a malicious action These bot programs churn away all day and night, prodding at millions of random IP addresses looking for holes to crawl through. — Jennifer Tanaka
The term Chatbot is closely related to chat bot and chatterbot. Chatterbot is more popular in relation to chatbot who talk a lot, and is not necessary very intelligent in processing the user answers. Chat bot is used by technical people who consider the word ‘bot’ as a normal term for ‘robotised actions’, and for them ‘chat bot’ is a special kind of bot. The term Chatbot is actually the most popular amongst these three terms and has the broadest meaning.

Chat bot, chatbot or chatterbot, can be found on screens and in the virtual worlds, but also in the real world, for example holographically projected or as physical talking and responding puppet, toy or robot. Often, chat bot appears online and in instant messenger programs such as Windows Live Messenger, AOL Instant Messenger or Google Talk, where a chat bot is part of the buddy, contact or follow list of the human user. Chat bot appears on many other platforms as well, such as social networks (e.g. Facebook), virtual worlds (e.g. Second Life) or mobile devices (e.g. iPhone).
Interestingly, the as-yet unnamed conversational agent is currently an open-source project, meaning that anyone can contribute to the development of the bot’s codebase. The project is still in its earlier stages, but has great potential to help scientists, researchers, and care teams better understand how Alzheimer’s disease affects the brain. A Russian version of the bot is already available, and an English version is expected at some point this year.
Earlier, I made a rather lazy joke with a reference to the Terminator movie franchise, in which an artificial intelligence system known as Skynet becomes self-aware and identifies the human race as the greatest threat to its own survival, triggering a global nuclear war by preemptively launching the missiles under its command at cities around the world. (If by some miracle you haven’t seen any of the Terminator movies, the first two are excellent but I’d strongly advise steering clear of later entries in the franchise.)
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.
ELIZA's key method of operation (copied by chatbot designers ever since) involves the recognition of clue words or phrases in the input, and the output of corresponding pre-prepared or pre-programmed responses that can move the conversation forward in an apparently meaningful way (e.g. by responding to any input that contains the word 'MOTHER' with 'TELL ME MORE ABOUT YOUR FAMILY').[9] Thus an illusion of understanding is generated, even though the processing involved has been merely superficial. ELIZA showed that such an illusion is surprisingly easy to generate, because human judges are so ready to give the benefit of the doubt when conversational responses are capable of being interpreted as "intelligent".