Have you ever felt like an ad is following you online? You may not be paranoid because you’re not completely wrong.

Your online behavior can dictate what ads you see. Let me use a personal example. I lost my glasses a few weeks ago and I decided to try out Warby Parker, an online company that allows you try on spectacles before you buy. After I selected five pairs of glasses and requested them to be shipped to my doorstep, I logged on to Facebook. In my news feed, I was greeted by a Warby Parker ad for one of the pairs of glasses I chose. That ad followed me for days, stalking me on social media or any websites I visited. And these ads knew me, or at least the products I was considering.

Being a marketing professional, I knew that Warby Parker wasn’t really stalking me, they were just “remarketing” or “retargeting” me. Us marketers have something called “cookies.” No, not the chocolate chip kind. Cookies are pieces of code that websites use to track which pages you visit and your activity history. This information allows them to target specific people with specific products so you specifically buy them.

While business get a ton of information online, this strategy has been used for years. For example, Target used transactional data back in 2012 to send ads for pregnancy products in the mail to women. The catch? Some of the women weren’t even aware they were pregnant and Target was able to figure it out before they did thanks to all of this information.

Even if you’re not pregnant, the amount of data that is gathered about you continues to grow and get more detailed. This means you will see more targeted emails, ads, and content based on your digital behavior and history. While there are ways to be careful on what you share or do online, this data can be used to serve you better and improve your online shopping experience–if you don’t mind them watching.

This post is sponsored by Aztek, a web design, development, and digital marketing agency located in downtown Cleveland.