Massive networks of fake Twitter accounts - with the largest consisting of over 350,000 profiles - have been accidentally uncovered by scientists who were probing to see how people use the microblogging site.
Some of the accounts have been used to fake number of followers, send spam and boost interest in trending topics, researchers said.
On Twitter, bots are accounts that are run remotely by a person.
"It is difficult to assess exactly how many Twitter users are bots," said graduate student Juan Echeverria, a computer scientist at University College London, who uncovered the massive networks.
The research began by combing through a sample of one per cent of Twitter users in order to get a better understanding of how people use the social network.
However, the data revealed lots of linked accounts, suggesting one person or group is running the 'botnet'.
These accounts did not act like the bots other researchers had found but were clearly not being run by humans.
The research suggests earlier work to find bots has missed these types of networks because they act differently to the most obvious automated accounts, 'BBC News' reported.
Many bots are obvious because they have been created recently, have few followers, have strange user names and little content in the messages.
The network of 350,000 bots stood out because all the accounts in it shared several subtle characteristics that showed they were linked.
These included tweets coming from places where nobody lives; messages being posted only from Windows phones; and almost exclusively including quotes from Star Wars novels.
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