Why All The Huff About The Cookie? continued
The second is unique to the Internet where certain providers can actually create a cookie that is visible on multiple sites. DoubleClick is known for this and many companies use DoubleClick to serve banner type ads on their sites. DoubleClick can place small GIF files on the site that will allow DoubleClick to load a cookie on your machine. DoubleClick can then track your movements as you surf the web. It potentially can see the search words you type into search engines. Because it gathers so much information about you, DoubleClick can form very rich profiles. These are still anonymous, but they are very informative.
DoubleClick then went a step further by acquiring a company and threatening to link these rich anonymous profiles back to name and address information -- it threatened to personalize them, and then sell the data. That began to look like spying to most people, and that is what caused the concern.