Twitter is recovering from a challenging day yesterday when many celebrities, from former President Barack Obama and Bill Gates to Kanye West, presidential contender Joe Biden and Mike Bloomberg, were the victims of a major scam involved in soliciting donations to Bitcoin, according to CNN.

“We all feel terrible this happened,” Twitter CEO Jack Dorsey said. “We’re diagnosing and will share everything we can when we have a more complete understanding of exactly what happened.”

The attackers posted tweets appearing to promote an apparent cryptocurrency scam and similar tweets soliciting donations via Bitcoin to their verified profiles on Wednesday.

“Everyone is asking me to give back, and now is the time,” a tweet from Gates’ account said, promising to double all payments to a Bitcoin address for the next half hour. Those tweets were later deleted.

Twitter officials said late yesterday they detected ” a coordinated social engineering attack by people who successfully targeted some of our employees with access to internal systems and tools.”

People assume what is posted by an account on Twitter is from the person who owns the account which increases the likelihood of a scam being successful, according to Axios.

This hack was especially alarming due to the number of world leaders who use Twitter. That includes President Donald Trump who often tweets major policy decisions. As a result, any such hack could, potentially, lead to a catastrophe. The hack also kept all verified users from tweeting for several hours.