Porn sites have been accused of hosting revenge porn videos, by a woman whose sister found videos of her online that had been posted without her consent.
"Sophie" said she felt "violated" after sex videos featuring her were viewed hundreds of thousands of times when they were uploaded online.
Sophie's sister saw the images on Pornhub.
Pornhub said it "strongly condemns" revenge porn.
It added it had "the most progressive anti-revenge-porn policy in the industry".
Campaign group #NotYourPorn said such content allowed Pornhub owners MindGeek to make greater advertising revenues.
MindGeek said it did not seek "to monetize revenge porn, and we work swiftly to remove it if it is uploaded".
'Shocked and embarrassed'
Sophie - not her real name - told the BBC's Victoria Derbyshire programme she had been on a day out with her family 18 months ago when she had checked her phone to find missed calls and messages.
Her sister's partner had found videos of her on Pornhub - the world's largest porn website.
Sophie says one was on Pornhub's main content page and had over 600,000 views, though Pornhub dispute this.
"I felt shocked, embarrassed and violated," she said.
Sophie had previously made six videos with her ex-partner.
They broke up several years ago and she had not given anyone consent to put them online.
Within a week of her becoming aware of the videos appearing on Pornhub, they were taken down.
However, the appearance of those six videos on Pornhub gave someone the opportunity to create about 100 video clips, and these were subsequently uploaded to a number of porn sites.
Sophie went to the police. To date, no-one has been charged.
Kate Isaacs, from the #NotYourPorn campaign, said revenge porn was often labelled on porn sites as "amateur" or "home-made" content - two popular search terms for videos that were making sites more valuable for advertisers.
She now wants these sites to do more to delete such content as soon as they are made aware of it, and to prevent it from being reuploaded once taken down.
'The effect on my family'
By the time Sophie discovered the videos of her online, she was in a new relationship - and it placed a strain on the couple.
Her partner's friends made fun of him over her videos on Pornhub, she said.
Sophie also has a teenage daughter, who she said "hasn't been the same since".
Pornhub dispute one of the videos is Sophie and say it was filmed by a verified model.
Pornhub vice-president Corey Price said: "Content that is uploaded to Pornhub that directly violates our terms of service is removed as soon as we are made aware of it and this includes non-consensual content.
"In 2015, to further ensure the safety of all our fans, we officially took a hard stance against revenge porn, which we believe is a form of sexual assault, and introduced a submission form for the easy removal of non-consensual content.
"We also use a state-of-the-art third-party digital fingerprinting software, which scans any new uploads for potential matches to unauthorised material and makes sure the original video doesn't go back up on the platform."
MindGeek told the BBC it was "not looking to profit off of illegal content or content that violates our terms of service.
"It's not in our best interest to host and gain revenue from this type of illegal content. We seek to provide users with a safe space to share and consume content," it added.
"The last thing we want is to undermine this by allowing revenge porn on our sites."