Donald Trump's Twitter account has lost hundreds of thousands of followers after the company purged fake accounts.
The site is getting rid of accounts that it says are fraudulent, and all of the biggest accounts are losing vast numbers from their follower counts.
The president has lost at least 300,000 followers from his controversial Twitter account already.
Twitter is no longer counting as followers any accounts that have been locked because of suspected fraud, boss Jack Dorsey posted on Thursday. Locked accounts had already been kept out of Twitter's daily and monthly active user figures.
The accounts are locked if Twitter detects unusual behavior such as a burst of activity after months of dormancy.
The new policy could be substantial for some Twitter users because follower totals serve as a top selling point when celebrities and so-called social media influencers negotiate deals with advertisers. For other users, follower counts are a point of pride.
The purge is affecting all large accounts, and it is not yet clear whether Mr Trump is being hit in any different way to the average. Katy Perry, whose Twitter account has the most followers of all, lost more than 2.8 million followers on Thursday, a 2.6 percent fall from the day earlier.
As the change went into effect, Twitter's "@Twitter" account lost 12.4 percent of its followers compared with Wednesday, the steepest drop among the top 100 accounts by followers, according to Keyhole data.
Tech executive Elon Musk saw the smallest dip, 0.3 percent, or about 71,000 followers. The median decline in the top 100 was about 734,000 followers, according to the data. Twitter said its service-wide average drop was expected to be four followers.
Twitter declined to provide additional data. Keyhole specializes in capturing data from Twitter and Instagram and selling reports to businesses.
Financial analysts have applauded Twitter's efforts to better limit misuse, saying that it could pay off with greater usage long term.
Additional reporting by agencies
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