Let me put your mind at ease: this isn’t spyware, and it’s not malicious.
It may be a little creepy, but there’s no intent other than marketing.
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- A technique called “remarketing” allows advertisers to show ads for things you’ve previously looked at.
- The technique targets your computer, not you as an individual.
- Clearing cookies periodically, or using an ad blocker, may help.
- Ads that seem to follow you are benign and nothing to be concerned about.
What you are seeing is an advertising technique called “remarketing.” It’s used by advertising networks, which are companies that websites contract with to present the advertisements you see. Most ads on Ask Leo!, for example, are provided by Google.1
It works like this:
- You visit a shopping site, or a site that offers some kind of service. This site may or may not show ads, but they do include content from an advertising network.
- The advertising network places a cookie on your computer. That cookie contains information to the effect of, “This computer was looking at X,” where X is the product or service offered by the site you’re visiting.
- Eventually, you move on to another website — a site that also displays ads, and coincidentally uses the same advertising network as the site we started at.
- That advertising network is given its own cookie back — the one that says, “This computer was looking at X” — and as a result, elects to show you ads for X.
There are several variations and I’m sure that the implementation is generally more complex than I’ve outlined above.
As a concrete example, I often visit the website of the hosting company I use, LiquidWeb.com — it’s just part of my daily activity as I manage the server that hosts my web sites. For the longest time, I saw ads for LiquidWeb as I moved on to other sites on the internet. The advertising network had no way to know that I was already a customer.
Advertising and tracking
I get that it feels a little like someone is following you. It’s like you visited a jewelry store, and as soon as you left, someone started following you, pestering you to purchase from that store. “I know you’re interested, because you came into the store and looked at this ring. Here it is again. Are you sure you don’t want to buy it?”
Technically, this type of tracking isn’t tracking you as an individual; it’s just a side effect of the places your computer has visited. Any computer that happens to view product X will likely see ads for X as they visit other sites.
So it’s your computer, not you personally, that this happens to. Move to a different computer and it’s possible you’ll see a different set of ads. If you don’t, it’s because your activity on that second computer was similar to that on the first — i.e., you looked at X on both, and thus will see ads for X on both.2
I’d be shocked if this kind information was kept very long. There’s a very good chance that simply clearing cookies3 will cause the remarketing system to forget what your computer has seen and begin the process again.
It’s certainly not spyware, and it’s definitely not malicious software on your machine. It’s simply advertisers leveraging how the internet and web browsers work by showing you ads for things you’ve shown an interest in.
There’s nothing you can really do about it without using an ad-blocking solution.
I know it makes some people uncomfortable, and understandably so, but ultimately, there’s really nothing to be concerned about here.
1: Except for ads I place manually, typically for my own books and services.
2: Technically, it’s even more granular than that. Since cookies are kept separately for each browser, it’s generally enough to switch to a different browser to see different ads.
3: Depending on how you clear cookies, this technique can include side effects like getting logged out of all the sites to which you are currently logged in.