E-mail spambots harvest e-mail addresses from material found on the Internet in order to build mailing lists for sending unsolicited e-mail, also known as spam. Such spambots are web crawlers that can gather e-mail addresses from websites, newsgroups, special-interest group (SIG) postings, and chat-room conversations. Because e-mail addresses have a distinctive format, such spambots are easy to code.
A number of programs and approaches have been devised to foil spambots. One such technique is address munging, in which an e-mail address is deliberately modified so that a human reader (and/or human-controlled web browser) can interpret it but spambots cannot. This has led to the evolution of more sophisticated spambots that are able to recover e-mail addresses from character strings that appear to be munged, or instead can render the text into a web browser and then scrape it for e-mail addresses. Alternative transparent techniques include displaying all or part of the e-mail address on a web page as an image, a text logo shrunken to normal size using inline CSS, or as text with the order of characters jumbled, placed into readable order at display time using CSS.
Forum spambots surf the web, looking for guestbooks, wikis, blogs, forums, and other types of web forms that it can then use to submit bogus content. These often use OCR technology to bypass CAPTCHAs. Some spam messages are targeted towards readers and can involve techniques of target marketing or even phishing, making it hard to tell real posts from the bot generated ones. Other spam messages are not meant to be read by humans, but are instead posted to increase the number of hyperlinks to a particular web site, to boost its search engine ranking.
One way to prevent spambots from creating automated posts is to require the poster to confirm their intention to post via e-mail. Since most spambot scripts use a fake e-mail address when posting, any email confirmation request is unlikely to be successfully routed to them. Some spambots will pass this step by providing a valid email address and use it for validation, mostly via webmail services. Using methods such as security questions are also proven to be effective in curbing posts generated by spambots, as they are usually unable to answer it upon registering.
A Twitterbot is a program used to produce automated posts on the Twitter microblogging service, or to automatically follow Twitter users. Twitterbots come in various forms. For example, many serve as spam, enticing clicks on promotional links. Others post @replies or automatically "retweet" in response to tweets that include a certain word or phrase. These automatic tweets are often seen as fun or silly. Some Twitter users even program Twitterbots to assist themselves with scheduling or reminders.