Many of the accounts, which mostly used footage from CNN, but also employed some video from Fox News, exploited a YouTube feature that automatically creates channels on certain topics. Those topic channels are then automatically populated by videos related to the topic — including, in this case, blatant misinformation. YouTube has now shut down many of the accounts.

YouTube's own algorithms also recommended videos from the channels to American users who watched videos about US politics. That the channels could achieve such virality -- one channel was viewed more than two million times over one weekend in October -- raises questions about YouTube's preparedness for tackling misinformation on its platform just weeks before the Iowa caucuses and points to the continuing challenge platforms face as people try to game their systems.

In recent years, YouTube, which is owned by Google, has taken steps to increase the likelihood users will be recommended videos from what it determines as authoritative sources, like news outlets.