YouTube promoted conspiracy theory videos claiming the 2017 Las Vegas mass shooting was a hoax, resulting in distress to survivors and victims' families. 

YouTube's recommendation algorithm was accused of amplifying misinformation and fake news about the Mandalay Bay hotel shooting in which 64-year-old Stephen Paddock killed 58 people. Some of the conspiracy theories promoted on YouTube include claims that the shooting was staged, that the shooter was not the actual perpetrator, and that the government was involved in a cover-up. 

Promoted on YouTube, the videos were picked up by Google's search engine and spread more widely. 

Google's failure of moderate content on its platforms responsibly prompted outrage from survivors and families. Furthermore, some victims reported being harassed online by conspiracy theorists.

Initially, YouTube defended its performance, though it eventually acknowledged there was "still more work to do" and updated its search algorithms to better promote reputable sources.

The fracas highlighted the power of recommendation systems in amplifying misinformation, including after mass shootings, and the inadequacy of Google's content moderation systems. 

It also underscored the need to balance free speech with responsible content moderation during breaking news events.