  Conspiracy theories have flourished on social media, raising concerns that
such content is fueling the spread of disinformation, supporting extremist
ideologies, and in some cases, leading to violence. Under increased scrutiny
and pressure from legislators and the public, YouTube announced efforts to
change their recommendation algorithms so that the most egregious conspiracy
videos are demoted and demonetized. To verify this claim, we have developed a
classifier for automatically determining if a video is conspiratorial (e.g.,
the moon landing was faked, the pyramids of Giza were built by aliens, end of
the world prophecies, etc.). We coupled this classifier with an emulation of
YouTube's watch-next algorithm on more than a thousand popular informational
channels to obtain a year-long picture of the videos actively promoted by
YouTube. We also obtained trends of the so-called filter-bubble effect for
conspiracy theories.
