SAN FRANCISCO -- Hundreds of thousands of disturbing videos of young children have been posted online, not in some dark corner of the internet, but on YouTube. 

The website is finally cracking down. It was a bottom-line decision.

Under pressure from advertisers, YouTube -- owned by Google -- removed more than 150,000 videos with images of children apparently being assaulted.

"At the end of the day, large tech companies are run by the bottom line, and I think YouTube has been an incredibly successful platform for Google, and they have simply not paid enough attention to some of the bad stuff that happens on that platform," said James Steyer, CEO of Common Sense Media.

YouTube began paying attention as advertisers pulled their ads, complaining about child-endangering videos.

In a statement Tuesday, YouTube said:

"Over the last few months we've taken deliberate steps to tackle many of the emerging challenges around family content on YouTube. In the past week, we've taken aggressive action, including removing over 150,000 videos from our platform that do not belong on YouTube, turning off inappropriate comments from over 625,000 videos, terminating hundreds of accounts and adding age-gates for videos that are clearly geared towards mature audiences. Beyond that, we have removed ads from over 2 M videos and over 50k channels that masquerade as family-friendly to reduce the incentive to produce this content."

"It's a new type of child abuse -- child sexual abuse exploitation," said Mary Pulido, executive director of the New York Society for the Prevention of Cruelty to Children. "Children can't unsee something. Once they look at an image, it is there in their brains forever."

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