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Sat, Oct. 19

How do companies know how to target ads to me?

Q. When I look at an ad in an email, I often get additional email advertising similar products. How do they know I looked at the message?

A. Unfortunately, that is a complex question. A common way is to insert a hidden image. When that image is opened, it sends a message back to the sender. The sender does not get any private information about you other than the fact that your email address opened a particular message. Some supervisors or committee chairs have used this software to see if employees or members read their messages.

The major browsers like Gmail and Firefox try to block such images as spam, but some software can get the images through. A simple way to stop such messages is to remove your address from the mailing list for companies that send such follow-ups, but then you won't see their special ads.

Newer software like PixelBlock tries to stop such images and are generally given positive ratings by users. That program is currently available as an extension for Gmail. If installed, it adds a small red icon at the right of the sender's name if the message includes such tracking images. Clicking on that icon opens a small window indicating how many such images were blocked in that message. Ugly email is a similar extension that is available for Chrome and is being developed for Firefox. [See or]

Another way to control such tracking is to go to the settings for your browser. Under "Images," there is usually an option that can be checked if you want to be asked before any external images are displayed. Tracking images should be included, but those that add visual appeal would also evoke a question.

In the long run, the key question is whether blocking such tracking is worth the effort. You could try PixelBlock to see how much of a problem it is.

The Prescott Computer Society (PCS) is a PC-based users group founded in Prescott over 25 years ago. Our monthly Saturday meetings help you get more out of your computer while keeping it safe from virus attacks. For further information, please visit us at

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