Even been haunted by an online ad for an item you researched or bought? Targeted ads were designed to follow you around everywhere. Here's how to banish them.

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Online ads have always been annoying, but now they’re worse than ever.

Consider what happens when you shop online for a wristwatch. You peruse a few watch websites and the next thing you know, a watch advertisement is following you everywhere. On your computer, it’s loading in your Facebook feed. On your phone, it’s popping up on Instagram. In your web browser, it’s appearing on news sites that have nothing to do with watches. Even if you end up ordering the watch, the ads continue trailing you everywhere.

They’re stalker ads.

And they are a symptom of how online ads are becoming increasingly targeted and persistent. Tracking technologies like web cookies are collecting information about our browsing activities from site to site. Marketers and ad tech companies compile that data to target us across our devices. And trackers are now so sophisticated that they can see when you are thinking about buying something but don’t follow through — so they tell the ads to chase you around so you make the purchase.

To the ad industry, targeted ads are better for people than the old days of randomly blasting commercials.

“The content isn’t free, so what would you rather see?” said Sarah Hofstetter, the chairwoman for the ad agency 360i. “Ads that are at least trying to be of interest to you, or ads that are spray and pray?”

That’s a fair point. On the other hand, these creepy ads can be extremely annoying, especially when they make incorrect assumptions. They are another example, along with obnoxious auto-play videos and internet trolls taking over internet comments, of how a few bad actors are breaking the integrity of the web.

Stalker ads also raise privacy concerns. A 2012 survey by Pew Research Center found that 68 percent of internet users did not like targeted advertising because they do not like having their online behavior tracked and analyzed. Your browsing history can reveal a lot about you, including your health issues, political affiliations and sexual habits.

Fortunately, I have good news. After several years of interviewing internet companies and privacy experts and testing many web tools, I finally managed to make my stalker ads go away.

Why are ads stalking me?

Before you try to exorcise targeted ads, it helps to understand what’s going on behind the scenes.

Let’s say you are shopping online for a blender. You load a webpage for a blender from Brand X, then close the browser. The next time you open the browser, ads for the blender are following you from site to site. They’re also showing up in some of your mobile apps like Facebook and Instagram.

When you visited Brand X’s website, the site stored a cookie on your device containing a unique identifier. Brand X hired multiple ad tech companies to do its marketing. The ad tech companies embedded trackers that also loaded on Brand X’s website, and the trackers took a look at your cookie to pinpoint your device.

The trackers can tell if you are interested in buying something. They look for signals — like if you closed the browser after looking at the blender for awhile or left the item in the site’s shopping cart without completing the purchase. From there, the ad tech companies can follow your cookie through trackers and ad networks on various sites and apps to serve you an ad for the blender.

Hofstetter said that among ad tech companies, there are good actors and bad actors. The good ones will try to minimize the chances of annoying you by showing you the blender ad only a few times and stopping if they detect that you made the purchase. The bad ones only care to persuade you to buy the blender, so they will relentlessly serve you the ad and not bother to determine whether you already bought it.

Things get extra messy when brands employ multiple ad tech companies that employ different approaches. Perhaps one ad company finished serving you the blender ad after a few times on Facebook. But elsewhere on the web or inside another app, another ad tech company served you that same ad endlessly.

What are some easy ways to sidestep stalker ads?

Here are a few simple steps you can take if you are being pestered by an ad and want that to end:

— Periodically, clear your cookies. Ad trackers will have a tougher time following you around if you delete your cookies on each of your devices. Apple, Google and Microsoft have published instructions on how to clear data for their browsers Safari, Chrome and Edge.

Reset your advertising ID. In addition to cookies, Android and Apple phones use a so-called advertising ID to help marketers track you. You can reset it whenever you want. On Android devices, you can find the reset button in the ads menu inside the Google settings app, and on iPhones, you can find the reset button inside the settings app in the privacy menu, under advertising.

Periodically purge your Google ad history. Google offers the My Activity tool, myactivity.google.com, where you can take a deep look at the data that Google has stored about you, including the history of ads you have loaded, and choose the data you want to delete.

If possible, hide the annoying ad. On some web ads, like those served by Google and Facebook, there is a tiny button in the top-right corner that you can click on to hide the ad.

How do I bring that up a notch?

There are more extreme methods to take if you want to prevent targeted ads from ever following you around. But this isn’t for the faint of heart: In my experience, you have to take all, not just some, of these steps to get the pesky ads to leave you alone forever.

Install an ad blocker. For your web browser, you can install add-ons that block ads. My favorite one for computer browsers is uBlock Origin, and on iPhones I recommend 1Blocker X. (For Android users, Google banned many ad blockers from its official Play app store, so the simplest way to block ads is by using a private web browser.)

On mobile devices, use a private browser. Firefox Focus, DuckDuckGo and Ghostery Privacy Browser are privacy-centric mobile browsers that include built-in ad and tracker blocking. These are handy when you want to do a discreet web search. (They can be impractical to use as everyday browsers because the built-in blockers can break important parts of websites.)

Install a tracker blocker. Tracker blockers detect snoopy code on websites and prevent them from loading. My favorite tracker blocker for desktop and mobile systems is Disconnect.me.

Wherever you can, opt out of interest-based advertising. Tech companies including Google, Facebook, Twitter and Apple offer instructions on opting out of receiving ads based on your interests.

It will probably take you a couple of hours to set yourself up to prevent ads from haunting you. I gradually made all these changes to my devices and internet accounts over the last few years and only recently stopped seeing targeted ads. It was a grueling process.

But I’ve been happy with the results. Those wristwatch ads that once followed me are gone. And recently, I was served an ad for 7-11 on Instagram.

Was that ad irrelevant to me? Yes. But was it a sign that I was no longer being well tracked? Also yes. I confess I was pretty happy to see it.

[Related: Read more stories about about protecting your sensitive personal information, data collection and security breaches.]