The worst day in Twitter's history.
That's how Twitter's CEO described the hacking attack.
About 4 in the afternoon on Wednesday, some of the biggest Twitter accounts in America were hacked.
Among them, U.S. Democratic presidential nominee Joe Biden and former President Barack Obama, as well as Bill Gates, Elon Musk,and the official accounts of Apple and Uber.
The scam accounted asked followers to send Bitcoin, saying they would send back double the money.
Soon after, the list of victims went on.
Twitter quickly removed many of the tweets, and eventually disabled verified users' accounts from posting.
But so far, it is not clear who the scammers are and how they hacked the accounts, despite strong passwords and an authentication system.
Twitter says it is investigating the problem.
The original Tweets have been deleted, but similar Tweets have been appearing.
Following the security incident, the company's shares fell more than 3 percent in extended trading.
Lee Kyung-eun, Arirang News.