Russia is gaming Youtube's algorithms by intentionally generating response data that links disparate videos. Whenever a user views a set of videos in a single session, those videos become linked as a chain of behavioral responses. If you want extreme propaganda to show up when people watch cat videos, just run a bunch of bots (or cheap human workers) to surf Youtube with a list of videos. The list would be something like this:
- Cat video #1
- Extremist propaganda video #1
- Cat video #2
- Extremist propaganda video #2
- Cat video #3
- Extremist propaganda video #3
Now you've got a session of 6 watched videos that link cat videos to extremist propaganda videos. Youtube's behavioral targeting algorithms form a link between the two, so that when you go watch Cat video #2, you'll see extremist propaganda videos in your feed.
This is part of what Mueller is talking about when he says Russia is hacking our Democracy. They are gaming social media and using it against us.