A stream of racist and anti-Semitic tweets were posted from the account of Twitter CEO, Jack Dorsey, after it was reportedly hacked on Friday, allegedly by a group called ‘Chuckle Squad’. Confirming the security breach, Twitter said that the company has initiated an investigation into the issue, and assured that the account is now secure and back under Dorsey’s control. All 17 tweets and 6 re-tweets made by the hackers have since been deleted.

In a follow-up tweet, Twitter also claimed that its own internal systems were not compromised by the hackers. According to the company, the account was hacked because the phone number associated with Dorsey’s account was compromised “due to a security oversight by the mobile provider. This allowed an unauthorized person to compose and send tweets via text message from the phone number”.

It’s not immediately known as to how the account was compromised, but according to some online reports, the rogue tweets were apparently sent via Cloudhopper, a service Twitter bought in 2010 to bolster its SMS service. According to The Verge, the service works by posting to Twitter any text message sent to 404-04 from phone numbers linked to people’s Twitter accounts.

As pointed out by the report, Chuckle Squad has been on a hacking spree of late, attacking the Twitter accounts of a number of celebrities and public personalities over the past week, including beauty vlogger James Charles, Shane Dawson and Comedian King Back. While rogue AT&T employees were thought to have been behind the earlier hacks, it will be interesting to know how the hackers got access to Dorsey’s phone number.