The "volume of fake account deletion, albeit good for longer term, raises uncertainty on near-term user growth expectations," wrote Bloomberg Intelligence analyst Jitendra Waral.
Twitter's stock had gained 94 per cent this year as of Friday's close, and Waral said the "risk to daily user growth should be low as the company has underscored low activity on the deleted accounts."
A Twitter spokesman said the Post's numbers confirm what the company had released on June 26 and "we have not and do not include spam accounts that we have identified in the active user numbers that we report to shareholders."
The company, in its first-quarter earnings report, also highlighted that the number of reported monthly active users would be "negatively impacted" by the continuing effort to rid the service of fake accounts.
"Most accounts we remove are not included in our reported metrics as they have not been active on the platform for 30 days or more, or we catch them at sign up and they are never accounted," Chief Financial Officer Ned Segal wrote in a tweet. "If we removed 70 million accounts from our reported metrics, you would hear directly from us."
Improvements to Twitter spam and fake account detection follow criticism that the service allowed harassment and manipulation to run rampant, as the company prioritized user and revenue growth over safety.
Lawmakers berated Twitter for how long it has taken the company to discover the millions of tweets from Russian-linked accounts that meddled in the US elections.
A former employee told Bloomberg last year that in early 2015 the company discovered a vast number of accounts, most of which were inactive or fake, with IP addresses in Russia and Ukraine, but failed to delete them.
Twitter rose 6.8 per cent last week, coinciding with a positive note from Wells Fargo analyst Peter Stabler, touting the company's success with video content. The shares declined 4.9 per cent to US$44.37 ($64.80) at 1:40 p.m. Monday in New York.