All they had to do was append a tracking code to their emails.

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Best of all, you don't have to worry about entering a product tracking code every time you download and install a copy on a computer.

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In that instance, Google used special computer code to install tracking files known as cookies on some people's computers even if the device was set to block such tracking.

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For example, when a user visited a website that had code for one tracking technology, the data collection would call out to and trigger other tracking technologies that weren't embedded on the site.

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The Journal in February reported that Google was using special computer code to install tiny tracking files, or "cookies, " on some people's computers, iPhones and iPads, even if the devices were set to block this kind of tracking.

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On the other hand, a small group of Samsung engineers has been working on medical applications of eye tracking, using open source code from Eyecan and the Not Impossible Foundation.

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While wandering the halls of Mobile World Congress, we came across NUIA (Natural User Inter Action), a German company whose software is designed to make it easier for developers to code apps that make use of eye tracking sensors, such as Tobii's.

ENGADGET

Today, a single Web page can contain computer code from dozens of different ad companies or tracking firms.

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Oracle has two versions of financial-tracking software, three sets of code for customer data and dozens of niche products.

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The other half worked on the back end, crunching computer code to build systems for order-processing, distribution and inventory flow and to integrate a new Web site tracking system with the existing ones.

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