Joe Biden, Elon Musk, Jeff Bezos and other high-profile Twitter accounts were the target of a widespread hack to offer fake bitcoin deals Wednesday in one of the most prominent security breaches on a social media site.

Accounts for former President Barack Obama, Microsoft co-founder Bill Gates, musician Kanye West and both Uber and Apple also posted similar tweets, all instructing people to send cryptocurrency to the same bitcoin address. The tweets were removed throughout the afternoon shortly after being posted to the accounts.

"This is a SCAM, DO NOT participate!" Cameron Winklevoss, a bitcoin investor and co-founder of Gemini, wrote of Musk's tweet.

There have been hacks of high-profile individual accounts on Twitter before, including Twitter CEO Jack Dorsey last year. But the widespread nature of this attack suggested an unusually broad access to internal controls. While it was unclear how the attacks originated or why they dragged on for hours, some cybersecurity experts speculated that someone may have gained access to internal Twitter controls that allowed them to take over accounts and post on their behalf.

"This is massive," said cybersecurity expert Rachel Tobac, who is chief executive of SocialProof Security. "This is most likely the largest attack I've ever seen. We are extremely lucky that these attackers are monetarily motivated and not sowing mass chaos all over the world."

It also partly shut the social network down. Users with the check mark to indicate their accounts were verified by the social media company reported they weren't able to tweet Wednesday afternoon.

Twitter spokeswoman Aly Pavela said earlier in the day that the company was investigating. The company said in a tweet it was "taking steps to fix" the security breach and would provide an update.

The breach will make it more difficult to verify the authenticity of messages on the service, cybersecurity experts warned. That could have wide-reaching implications for politicians, celebrities and brands that rely on Twitter as an essential channel for communication.

"The problem is that we all rely on Twitter as this public space that is safe and secure, and we know that the tweets that someone like a Joe Biden is sending out are authentic," Harper Reed, an entrepreneur who served as the 2012 Obama campaign chief technology officer. "Twitter has proven to us that may not be true."