Twitter accounts controlled by machines instead of humans that spit out tweets automatically using computer programs. Some of these robot accounts are able to tweet or retweet hundreds of posts within minutes. Most of the robotic accounts are used by spammers to send tweets designed to find their way into the occasional search results or discussion threads. One reason these fake accounts exist is the vibrant gray market in buying and selling Twitter accounts with large numbers of followers. Just like lists of working email addresses that can be sold to marketers, Twitter accounts with thousands of followers can fetch good prices. Another reason there are so many robot accounts out there is because they are easy to create and automate as Twitter allows automatic tweeting using third-party applications. The proliferation of robot accounts has led to accusations that the Twitter world may be populated by millions of accounts with questionable legitimacy.