They follow me everywhere: that cute pair of boots I drooled over for an hour on my favorite e-commerce site. No matter where I travel on the Internet, they’re there, staring into the depths of my soul — and my wallet.

But how do they do it? The answer, in a word, is retargeting. Retargeting is one of the most effective — and, let’s just say it: scary — weapons in today’s arsenal of digital marketing techniques.

It all starts with “cookies,” those little scraps of code that are stored on a person’s web browser and used to track and share their behavior. When I visited that e-commerce site — and spent an hour drooling over the boots— the website attached a cookie to me, like a sticky note stuck to my back that read, “hey, everybody, this gal really, really loves cowgirl boots.” Being thus branded, no matter where I went, I could be recognized — and served the same ads over and over again until, presumably, I caved and bought some darn boots.

And that’s how it works, folks. Retargeting keeps your brand front and center, keeping all your “window shoppers” engaged until they’re ready to buy.

These taunting, intelligent banners can go a step further with “dynamic creative ads,” which alter their messaging and creative in response to user’s online behavior, automagically serving ads uniquely tailored to individual users. For instance, using my boot example again, the site administrators might have inserted a little piece of code on the product page to let them know exactly which style of boot I was considering purchasing. Armed with this information, they could then serve me ads that showed not just any boots, but my boots.

The benefits of this technology to advertisers are obvious, but it can also benefit consumers by making sure the ads they are served are relevant to their interests. Sometimes, they can even help consumers land a better price — especially from airlines and hotel companies, which are notorious for haranguing would-be consumers with ads offering “travel deals” and “last-minute offers.”

They can be obnoxious, but I tend to think of the best retargeting ads like a friendly girlfriend, nudging me to treat myself to — oh, I don’t know — those boots I’m always admiring in the window. In the end, I’d rather that than some generic ad that has zero relevance to my interests.

(And, in case you’re wondering how the story ended, I did buy the boots — and they’re wonderful.)