It's a mix of your browser history and page content.

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How does it work?

Advertisers may collect data about your online browsing activity and use it to show you targeted ads (a process known as "behavioral advertising&quot .

You can prevent the companies listed below from showing you targeted ads by submitting opt-outs. Opting-out will only prevent targeted ads so you may continue to see generic (non-targeted ads) from these companies after you opt-out.

You may opt in to behaviorally targeted ads anytime by deleting your browser's cookies.
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For more.....
https://support.google.com/adsense/troubleshooter/1631343

I do this (deleting cookies) on a regular base, and beeing in Europe I could not manage to spend some money on DU. So the ads do not vanish but are chosen not along my previous clicks on whatever site but along some words in the original post I want to read here. Worst thing that happened: Ads for "dating" sites for Asian women came with reports to the terrible rapes in India. Remember that poor student who was raped to death? And then on the right side of that report there were barely covered huge breasts with almond eyes above and the words "Asian women want to love you" below.

I don't see what is so awful about targeted ads in the first place. People seem to get freaked out over it. I'm into bicycling, and I get a lot of ads for bicycle stuff - OMG, I've been violated!

But I can certainly understand how the ad-serving systems react to "hmmm... this one seems to delete history and cookies...."

Get a blocker like Ghostery (there are others, of course). Basic cookies just store information about the time and duration of your recent visits, your computer and browser type. Nothing all that serious. But Trackers are insidious little bastards, and they don't expire. They leave a trail of crumbs everywhere you go, and put out a virtual homing beacon (actually, there is a type of cookie called a "beacon," which sends out your info just to let the marketers know you're there). The track everything you do. That is why the ads on pages like FB are so uncannily accurate with the ads...they're watching what you surf, even when you're not using FB. Trackers send the information back to FB, which tailors the ads based upon your viewing of MarthasStewart dot com and/or NubianNymphs dot ru.

As if that's not bad enough, they persist even after you quit and relaunch your browser. Ad blockers and tracker blockers aren't difficult to install, and after a bit of tinkering (and explaining to your annoyed spouse why none of her shopping history is showing up -- easily fixable), blockers are really pretty darned convenient.

I never see ads, and my donation is small.
Well worth it, as so many other sites have way too many ads.

It doesn't take very much, either. Don't know what the minimum amount is, because I donate a bit more than whatever that might be.

assumes the poster is one of his fans and targets the ad accordingly. Anti gun posts are given NRA ads because guns are mentioned.

A few bucks for a star membership will get rid of them. It's worth it.

I'm all over that star membership thing. I don't care about the ads, but I need to support DU. And who could resist the prestige of being a star? Wait until I tell my friends!

that I don't even notice the ads anymore.