TV Derana YouTube channel got Hacked

•  On 29th August 2021, TV Derana YouTube channel got hacked by some hackers. 
• Now this is how their channel looks like;

• Whoever hacked this channel changed the name from TV Derana to Crypto News.
• As we can see this channel had over 3 million subscribers.
• Also in the videos tab there is a video about Bitcoin and Ethereum. 

• Every other video in that channel was Unlisted

What does Unlisted means? 

                       According to Google, "Unlisted videos and playlists can be seen and shared by anyone with the link. Your unlisted videos won't appear in the Videos tab of your channel homepage. They won't show up in YouTube's search results unless someone adds your unlisted video to a public playlist."

• This is  how an Unlisted video looks like in the Playlists tab.

• As we can see ; Under every video it has the symbol of Unlisted. 

When I see this as a Cyber Security undergraduate , I got a few questions in my head?

01. YouTube is a well-reputed company and it may be spending millions of dollars to keep it's security. Then How could a bunch of hackers were able to hijack a channel with 3 Million Subscribers?

02. Everyone talking about the physical side of this attack. But I need to know how did they did it in technical way. (Eg: They did  XSS or they did a MIMA phishing attack)

03. Is it an issue of channel owners; which lead them to this situation?

04. Are there any accounts other than TV Derana, which had been hacked by these hackers?

• I am sure for next 7 or 8 days this will be the topic in Sri Lanka. But will any one with technological knowledge can explain this attack? Now that is a real question. 
• We will see it in the near future.