Distributors of fake news used Google and Facebook's algorithms to their advantage to spread hoaxes in the midst of the Las Vegas massacre.
Retiree Stephen Paddock shot and killed 59 people at a country music concert on Sunday night (local time), and injured more than 500 more.
As word of the attack spread online, so did hoax stories, which relied on Google and Facebook's distribution structure to spread quickly.
A suspect misidentified on user-generated content website 4chan quickly became one of the top results on Google. The site is notorious for spreading fake news and racism.
Forbes reports a Facebook 'safety check' feature, activated for those in the area to identify themselves as safe for their friends and family, promoted stories from right-wing news sites Gateway Pundit and Blogspot, which also falsely identified the shooter.
The wrongly-accused suspect quickly circulated the internet, even making it onto some legitimate news sites.
Facebook's "trending topic" page also directed users towards stories by Russian propaganda websites, which cited religious affiliation as the motive behind the shooting.
Terrorist group Islamic State later issued a statement claiming responsibility for the attack, which has since been refuted by the FBI.
Google changed its algorithms in October 2014 so that non-journalistic sites could still be included in the "in the news" section.
This morning they told The Atlantic they took down the 4chan Google hits "within hours".
"The 4chan story was algorithmically replaced by relevant results. This should not have appeared for any queries, and we'll continue to make algorithmic improvements to prevent this from happening in the future."
In the past Facebook has employed extra staff to manually monitor the site during significant events, when there's a high interest in news content.
One thousand extra staff were hired for the United States election to weed out fake news.