Cyber safety expert and former undercover online detective Brett Lee has seen the worst there is to see on the internet.
But even he has been left confounded by a new and disturbing trend in online content which profits by targeting young kids with videos featuring popular children's characters in sexual and violent scenarios, reported news.com.au.
"As a detective, I used to pretend to be a child on the internet. Back in the early days of these sorts of investigations I would assume the identity of different children online. I did that for about five years and arrested a lot of child sex offenders," he told news.com.au.
"So I have a very good understanding, in some ways, of how it feels to be a young person on the internet."
Back then he was primarily hanging out on sites like MySpace and MSN Messenger, but the internet is a different place these days, and so is the experience on offer to young kids.
Mr Lee now works to educate parents and teachers about the dangers posed to young children who are left unsupervised on the web. Lately he has been warning of a disturbing trend in content known as elsagate.
The name refers to the princess character from popular children's movie Frozen who often appears in the bizarre content, either in cartoon form or as a person dressed as the character.
"We just came across this and thought it was really interesting," he said. "I've started talking to parents at schools about it over the past week, no parents I've spoken to are aware of it."
While many parents would likely be shocked to see the so-called elsagate videos, awareness of the perverted content has grown this year and YouTube — where most of it resides — has vowed to try harder to police the clips which at first glance look harmless but contain very disturbing themes.
"I'm not a tech expert, I'm a detective. But it appears this is slipping under the algorithms whereby it's thinking that it is content suitable for children but there is some very disturbing content there," Mr Lee said.
"A lot of it is subliminal, there's common themes like children getting left behind, getting injections, getting your foot caught in the escalator — things children would be fearful of," he said.
Other videos are decidedly more explicit in their content and involve things like simulation of sordid sexual acts and fetishes, dismemberment, cannibalism and kidnapping.
It is typically popular characters like Elsa the princess, Spiderman and Pepper the Pig who star in the clips, which often take a sinister turn.
Many of the accounts that post the videos are monetised and hence are making money from young kids watching these clips during a YouTube session, which are often being automatically suggested by the platform's algorithms.
But outside of the obvious financial incentives Mr Lee says there are serious questions that surround the abusive nature of elsagate content.
"I don't think anybody knows why they're doing this," he said.
The elsagate phenomenon has spawned dedicated forums on social media sites like Reddit where users post some of the most disturbing content they've come across.
One user posted an image this morning showing YouTube's search engine suggestion after typing in "nakid" — an apparent childlike attempt at writing "naked". The resulting suggestions promote searches for underage children.
Meanwhile this week, major advertisers have responded to the growing controversy by pulling ads from the streaming platform. Mars Inc. and Adidas are among the major brands to suspend advertising on YouTube while it cleans up the site.
It's been more than a decade since Mr Lee spent his days pretending to be a child on the internet to entrap criminals but he says nothing has changed when it comes to the unsavoury parts of human nature which manifest in the darker corners of the web.
"What has changed is the amount of children online," he said, and the access young kids have to a broad range of content.
When it comes to elsagate videos which hide in plain sight, it can be particularly difficult for parents to protect against.
"Filtering and monitoring software isn't going to stop this," Mr Lee said.
Ultimately, it's up to the tech giants like YouTube who host the content to enact better measures to block it, particularly on the version of the platform catered specifically to children.
Last week, YouTube released a statement saying it would focus on a crackdown on inappropriate videos on its platform, including child exploitation content which overlaps with the elsagate sub genre.
"In recent months, we've noticed a growing trend around content on YouTube that attempts to pass as family-friendly, but is clearly not," the company wrote in a blog post.
"While some of these videos may be suitable for adults, others are completely unacceptable, so we are working to remove them from YouTube."