Elon Musk said Friday that his plans to buy Twitter were "on hold."
The reason, he tweeted, was a probe into a "calculation that spam/fake accounts do indeed represent less than 5% of users."
Twitter had earlier this month estimated that false or spam accounts represented fewer than 5% of its 229 million monetizable daily active users.
Musk has previously said one of his priorities once the deal has gone through would be to make Twitter "better than ever" by "defeating the spam bots and authenticating all humans."
His announcement saw shares in the social media giant drop by 20% in early electronic trading before Wall Street opened.
Musk would have to pay a $1 billion termination fee to Twitter if he walked away, and the social media company could also sue him to complete the deal.