Ad sites and banners are annoying. They slow down your browsing experience and often have annoying ads that intrude on your browsing experience. What is disturbing about adware sites, however, is how they can take advantage of http loop-holes to track your browsing behavior through cookies.
An http cookie is a small piece of text stored on your local computer by a web browser. It can be placed there by a web server when you visit a web page. The purpose of these files is to store small pieces of information about your preferences, shopping cart contents, authentication, etc. This technology is good. They allow you to have store-front type experiences at sites like amazon and ebay. They don’t have any executable code so there’s no way they can store viruses and don’t cause you to have pop-ups. A server can only request the cookie data for a domain that they set, so a site can’t harvest all your cookies to see where you’ve been. They sound very simple and safe, right?
Well, advertising companies have figured out how to use this to track what you are doing. Let’s say that the ad company adware.me has banners on 4 different web sites: ePenguins.com, eHardware.com, eEK.com and eEgads.com. When you load a page on ePenguins.com there is a link to a banner on adware.me: banner1.adware.me. Your browser goes out and happily retrieves this image. While interacting with the adware.me site the web server places a cookie on your computer. It can put whatever it wants in their adware.me cookie, so it puts something down like “Linked from ePenguins.com @ 12:40p” (it knows this because banner1 is only called from ePenguins.com). You get the banner ad and move happily on in your surfing experience (provided that the banner doesn’t take over your screen for 30 seconds or something). Later on in the day you visit eEK.com. The banner situation repeats itself, but this time when you go to get banner2.adware.me you send the previous contents of the adware.me cookie. The adware.me server adds that you’ve visited the eEK.com site and now knows two sites where you’ve been.
Imagine what would happen if there were a big ad domain that had banners on thousands of sites. It could accumulate a huge amount of information about where you go. What if their formulas were more specific – it knew exactly what pages you were viewing on ePenguins.com. Imagine if their banners could dynamically choose what to show you based on the sites where you had been? Well – pretty much all of those things are true. This is an implementation of a “third-party cookie” or “tracking cookie”.
What do you do about it? I’ll tell you in my next article what I do to block parasites like this on my computer.
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