https://casparwre.de/blog/seo-scam/
TLDR it's an HTML 'cleaner' but has been injecting links into the cleaned HTML. Very clever/sneaky... really risky too.
Good read.
Yeah, sneaky and smart, but they got caught. I wonder of they could have they could have done it in a way that spread the links out to a larger, more general network that then pointed back to them and not get caught?