Major brands have begin pulling advertising from YouTube after it was reported that paedophiles are operating on the site and evading protection mechanisms.
Brands, including Mars and Lidl, have stopped advertising on YouTube on the eve of one of the biggest shopping days of the year, after they were alerted that they were appearing with videos exploited by paedophiles.
According to investigations by BBC News and The Times, there are estimated to be tens of thousands of predatory accounts leaving indecent comments on videos of children.
Some videos are posted by paedophiles and many are innocently posted by youngsters.
Some of the comments are said to be sexually explicit, while others reportedly encourage children posting the videos to perform sexual acts.
The BBC and The Times spoke to people from the site's "trusted flagger" scheme who report inappropriate content or behaviour by users to YouTube employees.
Some of the volunteer moderators told the BBC there could be "between 50,000 to 100,000 active predatory accounts still on the platform" while another told The Times there are "at least 50,000 active predators" on the site.
As well as trusted flaggers, YouTube also uses algorithms to identify inappropriate sexual or predatory comments.
However, the system is said to be failing to tackle the problem and paedophiles are continuing to comment on videos of children.
According to The Times, adverts for several major international brands, including a global sportswear brand and food and drink giants, appear alongside the videos, raising concerns that they could be indirectly funding child abuse.
Confectionery giant Mars said: "We are shocked and appalled to see that our adverts have appeared alongside such exploitative and inappropriate content.
"It is in stark contrast to who we are and what we believe.
"We have taken the decision to immediately suspend all our online advertising on YouTube and Google globally.
"We have stringent guidelines and processes in place and are working with Google and our media buying agencies to understand what went wrong.
"Until we have confidence that appropriate safeguards are in place, we will not advertise on YouTube and Google."
Lidl said: "We are extremely shocked and disturbed by the findings of this investigation and are grateful to have been informed about this.
"We have suspended all of our YouTube advertising with immediate effect.
"It is completely unacceptable that this content is available to view, and it is, therefore, clear that the strict policies which Google has assured us were in place to tackle offensive content are ineffective."
YouTube said it had noticed a growing trend around content "that attempts to pass as family-friendly, but is clearly not" in recent months and announced new ways it was "toughening our approach".
Johanna Wright, vice president of product management at YouTube, said in a blog: "We have historically used a combination of automated systems and human flagging and review to remove inappropriate sexual or predatory comments on videos featuring minors.
"Comments of this nature are abhorrent and we work... to report illegal behaviour to law enforcement.
"Starting this week we will begin taking an even more aggressive stance by turning off all comments on videos of minors where we see these types of comments."