Multiple artists including Justin Bieber, Drake, and Eminem were hacked on their YouTube channels. There were strange and improperly loaded videos posted by the hacker. A twitter account claimed they were responsible, but the person behind the account is unknown. Many artists have their information and work posted, so it can be accessed at all times.
To prevent this from happening again the security needs to be updated and information needs to be protected with strong passwords and two-factor authentification.