It's becoming increasingly common for internet criminals to hack legitimate websites and redirect those perusing 'adult sites' to illegal images of child abuse hosted there, according to the Internet Watch Foundation (IWF).
The outfit has received more than 227 reports of this happening over the past six weeks, sometimes with added bonus malware on top.
Websites are used to host secret folders of images without the website owners' knowledge, with the links then littered across legal porn sites.
The IWF is baffled by this, but perhaps it's down to hiding in plain sight: by directing innocent web users to these pages as well, it obscures those who are heading intentionally for the abusive pictures.
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"It shows how someone not looking for child sexual abuse images can stumble across it," IWF technical researcher Sarah Smith said.
"The original adult content the internet user is viewing is far removed from anything related to young people or children.
"We've received reports from people distressed about what they've seen. Our reporters have been extremely diligent in explaining exactly what happened, enabling our analysts to re-trace their steps and take action against the child sexual abuse images."
Anyone stumbling across illegal images should report them to the NSPCC immediately.