High-profile Twitter accounts, including those of Barack Obama, Elon Musk and Kanye West, have been hacked as part of a widespread cryptocurrency scam.
And the social media giant temporarily halted verified accounts from posting in an attempt to stem the cyber hijacking.
The accounts, which have large Twitter followings, were simultaneously hacked on Wednesday evening and a message posted encouraging users to send 1,000 dollars (£794) to a Bitcoin address.
In return, users are promised that their money will be doubled and returned to them.
Founder Jack Dorsey said: “Tough day for us at Twitter. We all feel terrible this happened.”
The message read: “I am giving back to my community due to Covid-19! All Bitcoin sent to my address below will be sent back doubled.
“If you send $1,000, I will send back $2,000!
“Only doing this for the next 30 minutes! Enjoy.”
Targeted accounts included Microsoft founder Bill Gates, Democratic presidential candidate Joe Biden and Amazon billionaire Jeff Bezos.
Kanye West’s account was hacked twice in the space of an hour with the same message posted.
A number of company accounts, including that of Apple and Uber, were also hacked with the message posted.
Most of the tweets were deleted within a number of minutes, but many had been retweeted thousands of times.
In a statement posted online, Twitter said: “We are investigating and taking steps to fix it. We will update everyone shortly.”
Dorsey later added: “We’re diagnosing and will share everything we can when we have a more complete understanding of exactly what happened.”
On Thursday morning Twitter said most accounts should be able to tweet again, but that “functionality may come and go”.
Users reported that those with verified accounts, marked by a blue tick, could not send tweets for a brief period – with those who tried shown an error message reading: “Something went wrong, but don’t fret – let’s give it another shot”.
The hacked messages were posted after several high-profile cryptocurrency companies’ Twitter accounts shared malicious links earlier on Wednesday.
Tyler Winklevoss, who founded cryptocurrency company Gemini alongside brother Cameron, tweeted earlier today: “WARNING: @Gemini’s twitter account, along with a number of other crypto twitter accounts, has been hacked.
“This has resulted in @Gemini, @Coinbase, @Binance, and @Coindesk, tweeting about a scam partnership with CryptoForHealth. DO NOT CLICK THE LINK! These tweets are SCAMS.”
His brother Cameron added: “ALL MAJOR CRYPTO TWITTER ACCOUNTS HAVE BEEN COMPROMISED.
“2FA / strong password was used for @Gemini account. We are investigating and hope to have more information shortly.”