He later cited bots as a reason to back out of buying the social platform. Now that the billionaire has completed the deal, he’s faced with the task of delivering on his promise to clean up the fake profiles that have preoccupied him and bedeviled Twitter since long before he expressed interest in acquiring it.

The challenge carries high stakes. The bot count matters because advertisers — Twitter’s chief revenue source — want to know roughly how many real humans they are reaching when they buy ads. It’s also important in the effort to stop bad actors from amassing an army of accounts to amplify misinformation or harass political adversaries.