Bill Gates, Elon Musk and Jeff Bezos are among many prominent figures targeted by hackers on Twitter in an apparent Bitcoin scam.
The official accounts of Barack Obama, Joe Biden and Kanye West also requested donations in the cryptocurrency.
A tweet from Bill Gates’ account said: “Everyone is asking me to give back.
“You send $1,000, I send you back $2,000.”
Twitter said it was a “co-ordinated” attack targeting its employees “with access to internal systems and tools”.
The company said in a series of tweets: “We know they [the hackers] used this access to take control of many highly-visible (including verified) accounts and Tweet on their behalf.”
Twitter added that “significant steps” were taken to limit access to such internal systems and tools while the company’s investigation was ongoing.Meanwhile, Twitter CEO Jack Dorsey tweeted: “Tough day for us at Twitter. We all feel terrible this happened.”
Twitter earlier had to take the extraordinary step of stopping many verified accounts marked with blue ticks from tweeting altogether.
Password reset requests were also being denied and some other “account functions” disabled.
By 20:30 EDT on July 15, users with verified account started to be able to send tweets again, but Twitter said it was still working on a fix.
Dmitri Alperovitch, who co-founded cyber-security company CrowdStrike, told Reuters: “This appears to be the worst hack of a major social media platform yet.”
On the official account of Elon Musk appeared to offer to double any Bitcoin payment sent to the address of his digital wallet “for the next 30 minutes”.
“I’m feeling generous because of Covid-19,” the tweet added, along with a Bitcoin link address.
The tweets were deleted just minutes after they were first posted.
However, as the first such tweet from Elon Musk’s account was removed, another one appeared, then a third.
Others targeted included: Kim Kardashian, Mike Bloomberg, Apple and the ride-sharing app Uber.
The Biden campaign said Twitter had “locked down the account within a few minutes of the breach and removed the related tweet”.
A spokesman for Bill Gates told AP news agency: “This appears to be part of a larger issue that Twitter is facing.”
Last year, Jack Dorsey’s account was hacked, but Twitter said it had fixed the flaw that left his account vulnerable.