After a massive “coordinated social engineering attack” on its internal systems to hijack accounts of some high-profile personalities Wednesday night, Twitter CEO Jack Dorsey early today morning tweeted that it was a “tough day for us at Twitter”.

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

In what appears to be the largest and most coordinated hack in Twitter’s history, the social media giant suffered a major security breach on Wednesday as hackers accessed its internal systems to hijack accounts of some of the prominent figures including US presidential candidate Joe Biden, former American President Barack Obama, billionaire Elon Musk, as well as that of Apple and Uber and used them to solicit digital currency.

Other compromised accounts include those of Kanye West, reality TV star Kim Kardashian, Michael Bloomberg, Microsoft co-founder Bill Gates, Amazon CEO Jeff Bezos and a number of cryptocurrency exchanges or organizations.

The compromised accounts, which count tens of millions of followers, sent a series of tweets proposing a classic bitcoin scam. Followers were told that if they transferred cryptocurrency to a specific bitcoin wallet, they would receive double the money in return.

As the security breach came to light, Twitter, in an extraordinary measure, disabled the ability to tweet from validated accounts for about two hours.