Hackers used credentials leaked online after numerous data breaches suffered by other companies. Users often chose weak passwords and share the same credentials across multiple websites. GitHub confirmed to have detected a large number of attempts to access users accounts. The hackers used lists of email addresses and passwords from other online services that have been compromised in the past, and tried them on GitHub accounts. GitHub has already reset the passwords of the affected accounts, at the same time it is suggesting users to adopt a proper security posture.”]
Source: https://securityaffairs.co/wordpress/48473/hacking/github-unauthorized-accesses.html