For all of Twitter's appeal, an awful lot of it is essentially white noise - people shouting at people shouting at bots. Indeed, there are a lot of automated bot accounts, whether simply retweeting related content on a particular subject, or just parroting customer service slogans.
In recent documentation filed with the SEC, Twitter clarified that the total number of bot accounts on its service amounted to 23 million out of its total 271 million user base. That's the equivalent of 8.5% of Twitter accounts being unmanned and regurgitating pre-programmed messages.
As Quartz points out, not all of these bot accounts are spam - many do perform a genuine customer service role, or a valuable information service, or whatever. Many though, let's face it, are spam and are completely and utterly useless.
The figures reported by Twitter were correct at the end of June 2014. Quartz also deduced from the disclosures that 7 million (2.5%) of Twitter's monthly active users access the service via third-party clients.
Update: Twitter has contacted us to point out that Quartz "erroneously called this stuff 'bots' when it wasn't at all". According to Twitter, the 23 million accounts are more accurately described as "having automatically contacted our servers for regular updates".