TechMan: On a Mac or PC? Websites know

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When we learned last week that travel booking site Orbitz.com shows higher-priced hotel choices to Mac users than PC users, inquiring minds wanted to know: "How do they know which computers I'm using."

It turns out that your computer is routinely ratting you out to sites you visit on the Internet.

When your browser contacts a site using the Hypertext Transfer Protocol (that's the http:// at the beginning of the Web address), it doesn't just ask to view the page. The browser also transmits information to the Web page's server.

The browser is known as the user agent because it "represents" the user in the Web transaction. Some of the information transmitted (such as whether you using a Mac or PC) is contained in the "user agent string."

User agent strings vary from browser to browser but almost all identify the browser being used, the version of the browser, the operating system of the computer and the version of the operating system.

You'll notice that the user string may not specifically name the brand of computer, but that can be readily determined from the operating system. If the operating system is OS X or earlier, the computer is probably a Mac. If it is Windows 7 or earlier, it is likely a PC. The browser could be Internet Explorer, Safari, Chrome, Firefox, Opera or many others.

So why does the server need to know what kind of browser you are using?

One reason goes back to a continuing bugaboo of modern computing -- the lack of standards.

Different browsers interpret Web pages differently, so a page designed for Safari it might not look "right" in Internet Explorer.

The user agent string also communicates to a Web page the size of the screen you will be viewing it on.

Many sites, such as post-gazette.com, have alternate designs for smaller screens. If you go to post-gazette.com on a cell phone, you will see a differently formatted page than at the same URL on your laptop or desktop.

So one lesson of the Orbitz case is to be aware that you are transmitting information about yourself every time you surf to a Web page.

And every time you give information online or offline -- be it registering a product, taking a survey, joining a website, or signing up for a credit card, loyalty card, social network -- that information could end up in a database somewhere and be for sale.

Taking varied information, putting it in a database and then looking for useful patterns and correlation is often referred to as "data mining," although that term has a more specific meaning in the computer science world.

In the advertising business, this is looked on as a good thing, allowing ads to be displayed that are more relevant to the consumer's needs and desires.

Other see it as a privacy issue.

No matter your view, as a consumer, learn from the Orbitz case. They know more about you than you might think.

And the purpose of collecting that information is to pry open your wallet.

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Read TechMan's blog at post-gazette.com/techman. Watch or listen to TechTalk at multimedia.post-gazette.com. First Published July 1, 2012 12:00 AM


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