The top trending video on YouTube Wednesday morning advanced a burgeoning conspiracy theory that a survivor of last week's shooting at a Florida high school was a "crisis actor."

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By 11 a.m. ET, the video had been removed from YouTube — but could still be viewed on other sites.

"This video should never have appeared in Trending. Because the video contained footage from an authoritative news source, our system misclassified it. As soon as we became aware of the video, we removed it from Trending and from YouTube for violating our policies. We are working to improve our systems moving forward," a YouTube spokesperson told CNBC.

Mary deBree, Head of Content Policy at Facebook, also said in statement that "we are removing this content from Facebook."