is quite simple.
bought advertisements, targeted for the site, bought from the site.
not involving the ad network middlemen. the problem with them in the first place is that any friggin site can have ad network ads in the first place and as result there's no CURATION whatsoever and quality of content doesn't really matter(only getting the viewer to the page matters! if the content is worse than the ad then that's a plus for the publisher too.. ).
the cancer of the modern internet is quite simply the ad networks - it makes it possible to monetize a site on the day one before a single human being looks at the site and thinks "do I want to pay ads to appear on this piece of shit?". it also leads to rather shitty content and just verbatim copied content propagating without reason.
then there's the cancer of the cancer: chained advertisement sites! you know, paying for clickbait advertisements that then only lead to pages that have MORE advertisements in an effort to pay for clicks that are supposed to be worth more directly just in adverts.
mobile slashdot sucks bigtime because of their advertisements. it makes it stutter even on galaxy note edge and I seriously doubt even the editors know what kind of advertisements get inserted(half a screen sized shit that is poorly coded making scrolling stutter). if they were advertisements bought from slashdot served _from_ slashdot with some sort of editiorial resemblance it wouldn't be half bad. now they only rely on miss clicks when scrolling. the stuttering makes the miss clicks even more likely!
all the browsers should just ship with ad blocking. but why do you think google came up with Chrome in the first place?