Someone just liked your tweet. Someone else followed you. Do you know them? No?

They could be among the nearly 48 million bots on Twitter, according to study released last week by the University of Southern California and Indiana University.

The study, which used more than 1,000 features to identify bot accounts on the site across six categories, estimated that between 9 percent and 15 percent of Twitter's active monthly users are bots. Using Twitter's most recent figure of 319 million active monthly users, that translates into 28.7 million to 47.9 million bots.

The higher-end figure is significantly higher than Twitter's own bot estimate. A Twitter spokesman declined to comment Tuesday other than to point to a Securities and Exchange Commission filing on Feb. 27. In the filing, Twitter restated its previous estimate that 8.5 percent of its active monthly users are automated accounts. According to Twitter's figure, just over 27 million of its accounts are bots.

The university researchers actually suggested that their 15 percent figure is a "conservative estimate" given the sophisticated nature of more complex bots, which could have been incorrectly identified as humans.

This is not the first time that Twitter has come under the spotlight due to bot accounts. A study from the University of Southern California last year found that 19 percent of election-related tweets during the study's period came from bot accounts.

First published, March 14 at 1:26 a.m. PT.
Correction, 5:20 a.m. PT: The calculation of the number of potential bot accounts has been fixed.
Update, 9:05 a.m. PT: Twitter's response has been added.

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