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Posted 8/11/2003 9:40 AM     Updated 8/11/2003 9:46 AM
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What your IP address tells about you
When you're surfing the Web, do you feel secure in the knowledge that you're anonymous? Don't.

Web sites have the ability to capture pieces of information about their visitors. The site knows the type of browser you're using, and its version number. It knows your operating system. And it knows your IP (Internet Protocol) number.

The first two are not a problem. Sites want to know your browser type so they deliver pages that work correctly with it. The same goes for your operating system. But the IP number raises privacy issues.

There are two types of IP numbers — public and private. A public IP number is unique. Like a telephone number, no one else has it. There are places on the Internet where you can identify the owner of an IP number. Conceivably, your visits to questionable Web sites could come back to haunt you.

The public IP number is actually an address. Public numbers are registered, so that Web servers know where to find them.

You have probably seen these numbers — their form is (that is, four numbers between zero and 255, separated by dots). For instance, the IP for my Web site, www.komando.com, is If you enter, you'll get to my site.

When you go to the Internet from home, you carry an IP number assigned to you by your Internet service provider. This generally is a public number. If you're using a dial-up modem, you probably are given a different or dynamic number each time you connect to the Net. But if you have broadband, you might have a permanent or static number.

Individual business computers are often better shielded. If you are on a network, the public number is assigned to a gateway. That is usually a company firewall or router.

The company system assigns a different set of numbers to internal computers. Those are private numbers, rather than public. They do not have to be exclusive; the guy down the street could be using the same numbers. Only the public number, which is assigned to your gateway, is exclusive.

Individual computers behind the firewall or router are not immediately identifiable. The IP number read by Web sites belongs to the firewall or router. But that doesn't mean the individual computer can't be identified. Company officials can track them. If an illegal act were committed with one of the computers, its identity could be learned through a subpoena.

Services such as Anonymizer (anonymizer.com) and Orangatango (orangatango.com) let subscribers hide their IP numbers when surfing the Web. These services encrypt and reroute subscriber's Web travels through their proxy servers. This way, sites cannot track a user's information. The cost is around $4 per month, or less when signing up for a year.

If you want to know what information you're disclosing to Web sites, use Privacy.net's analysis tool (privacy.net/analyze). Most people don't worry about disclosing this data, assuming they know about it. So much data is maintained on us that this seems pretty minor. And, other than IP numbers, it isn't personal.

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