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4Chan is an organised group that has been described on online message boards as "sick" and "horrifying stuff", according to the BBC.
Google, YouTube's owner, said most of the videos have been removed, but some could remain accessible for days as it sifts through the system to clean it up.
The attackers used popular celebrities such as Hannah Montana to lure YouTube users to the videos, but innocent footage soon turned into something much steamier.
Google said any account set up to attack YouTube in this way will be disabled, but it may take some time for video search results and thumbnail images to disappear from the site.