Twitter co-founder and chief executive Jack Dorsey’s account was hacked on Friday, and used to post a series of erratic and offensive messages.
A group referring to itself as the Chuckling Squad said it was behind the breach of Jack Dorsey’s account.
A spokeswoman for Twitter told the BBC that the site was urgently investigating.
The news comes with Dorsey and Twitter moving aggressively to clean up offensive and inappropriate content as part of a focus on “safety.”
The account, which has more than four million followers, tweeted out a flurry of highly offensive and racist remarks for about 15 minutes.
The messages – some posted directly by the @jack account, and others retweeted from other accounts – used the n-word and made anti-Semitic comments referencing the Holocaust.
A chat channel on Discord, a separate website, was apparently set up by the group to discuss and joke about the attack – but was quickly shut down.
The Chuckling Squad has taken credit for a number of attacks on high-profile Twitter accounts recently, including @Etika, an account belonging to YouTube personality Desmond Amofah, who died earlier this year in an apparent suicide.
It is as yet unclear how the attackers gained access, though it appears a vulnerability in a third party app could potentially have been to blame.
It is an embarrassing incident for Mr Dorsey, with many security experts questioning whether he, of all people, should have had the appropriate protections to stop such an attack being possible.