Kanye West and Elon Musk have been targeted as part of a major hack on high profile Twitter accounts.
Former U.S. leader Barack Obama, 2020 presidential hopeful Joe Biden, and Bill Gates have also been alerted to the security breach, according to multiple reports.
"We are aware of a security incident impacting accounts on Twitter," a representative for the site said in a statement posted on the micro-blogging platform's support account. "We are investigating and taking steps to fix it. We will update everyone shortly.
"You may be unable to Tweet or reset your password while we review and address this incident."
The hack appeared to be a bitcoin scam with messages posted to users' accounts asking followers to send them money.
Corporate accounts, including those belonging to Uber and Apple, were also hacked.
An Uber spokesman says: "Like many others, our @Uber account was hit by a scammer today. The tweet has been deleted and we’re working directly with @Twitter to figure out what happened."
The hack comes almost a year after Twitter CEO Jack Dorsey's account was hijacked by pranksters tweeting racial slurs and a bomb threat. The messages were quickly removed.
