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 on either, 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?”