Jack Dorsey’s official Twitter account, was hacked Friday. He is the CEO and Co-founder the same social media platform. The tweets contained erratic and offensive racial slurs, even suggesting an imminent bomb threat. The broadcast showed up around 2000 GMT on @jackaccount, with Twitter quick to respond, stating that his account had been “compromised.” This further demonstrates how potentially vulnerable high-profile social media accounts are.

The comments were deleted after 30 minutes.

According to Twitter, its own systems were not compromised and blamed an unnamed mobile operator.

Different sources claimed it to have been due to hackers using a technique called “sim-swapping” where hackers take over victims’ cell phone number, gaining access to apps. This is possible if the hackers have personal information on the victim, while other sources claimed that Dorsey’s 4.2 million subscriber account was hacked using Cloudhopper, which Twitter acquired in 2010.

A group calling itself “Chuckling Squad” has claimed responsibility and even a channel on Discord (a separate website) was setup by them to joke about the attack. It was later shut down. This is the same group responsible for a number of Twitter attacks last week, including beauty blogger James Charles, Shane Dawson, and comedian King Bach.

Friday’s incident recollected the events of a 2017 incident, in which a displeased Twitter contractor took Trump’s account offline for 11 minutes, leading to question security protocols at the company. Dosrey’s account was previously hacked as well. In 2016, a security company hacked his account and messaged “testing your security.”

The incident is a humiliating setback for Twitter, raising questions about vulnerability of high-profile accounts as the service hosts the world’s most powerful leaders, including that of President Trump, could be compromised; if a hacker was to access the account and make political claims or even start a war.

This hack also comes at a time when multiple social media platforms are under intense public scrutiny and pressure to implement content monitoring solution and policies, as they struggle in finding a balance between policing extremism and hate speech in order to create a forum of free expression.