Twitter Inc. (NYSE:TWTR) pleased investors last month with steady user growth, but a self-reported rise in automated traffic gave some pause for concern. Twitter now says it overestimated the number of monthly active users that might not, in fact, be actual users.

In a new filing, Twitter said that “up to approximately” 8.5 percent of its active user base consists of those who access the site through a third-party, or 23 million of its 271 million monthly active users, at the end of June. Twitter said last month that as many as 14 percent of its users were using third-party applications to access its service, meaning up to 38 million users weren't being served with ads. But the San Francisco-based company has largely reassured Wall Street since then, and its stock is up plenty.

Twitter said in an updated filing Monday that it now believes only 11 percent of its monthly users are using third-party apps. The company added that it was able to more accurately find  accounts that access the site's content without user input, after it “reviewed and refined” the processes it uses to detect “automated activity.” Such activity can be caused by third-party apps, or bots that use Twitter's API to download and send out automated responses.

Twitter bots aren't just the spam accounts that attempt to look like real users to gain followers and then tweet out paid links. Some, like @CongressEdits, act like a government watchdog, automatically notifying followers of edits made to Wikipedia entries from congressional computers. Developer Colin Mitchell has created a number of bots that respond to quotes from popular movies, like “Office Space” and “Beetlejuice.”


Spam or not, bots are of great concern to the site’s advertisers, who want to make sure that their ad money is going toward ads seen by real users. Twitter has not released official figures to discuss how many monthly active users were spam accounts.

An earlier version of this article erroneously reported that all users who used non-Twitter apps to download the site's data were bots. While some of those users may be bots, many are users who access the site through third-party software.