Twitter was hit with a widespread attack on 15 July that allowed hackers to take over an array of accounts including those of celebrities, politicians and billionaires such as Bill Gates, Kanye West, Joe Biden and Barack Obama, as well as Apple and other companies.

The attack, which security experts called the most significant hacking incident in Twitter’s history, began before 4pm EDT, when compromised accounts—many of them related to the digital currency bitcoin—began posting messages requesting money be sent to cryptocurrency accounts. The attacks quickly spread to additional, more prominent accounts, with the bogus messages sometimes receiving thousands of likes before they were taken down, only to be posted again a short time later, sometimes on the same account.