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How you get tracked on the 'Net: Part One

Jim Reavis
Network World on Security, 11/03/99

We currently seem to be in the midst of a Privacy Explosion. The concerns over Web site practices, technology developments and government policies are leading to both a rapid escalation in activism by privacy-rights advocates and a slew of new market entries into the privacy business. Before you go into a state of privacy apoplexy, it is important to understand the many different ways that you are and can be tracked on the Internet.

MAC address. The media access control address is the unique number burned into your network interface card. Guaranteed uniqueness is something highly desired by computer programmers. By having a value that they know will be unique and unchanged on every machine, they can use this value to simplify programming tasks. Microsoft was under the gun earlier this year for using a PC's MAC address to identify the owner of Microsoft Office documents. Although pilloried for this and forced to change the code to prevent this type of identification, it should be noted that this MAC address feature was partially responsible for apprehending Melissa Virus creator David Smith.

The MAC address can also be used to auto configure the machine's networking protocol address. Novell IPX, for example, has used the MAC address concatenated with the network segment's address for a very long time. The next generation of TCP/IP, IPv6, also has the capability to use the MAC address as a portion of the TCP/IP address. The main reason for using the MAC address as a portion of the protocol address is for ease of management. However, the side effect of this capability is an audit trail that can be difficult to avoid. Tying the MAC address to TCP/IP exponentially increases the ability to track a machine's activity, as the TCP/IP addressed is logged all over the Internet.

IP Logging. A station's IP address can be captured at several different places on the Internet. Web Server log files can be a rich source of information about the user that is browsing the site. Among the pieces of data that can be discovered are browser type and version, operating system type and version, length of visit, pages requested, and even the previous site you were at (known as the referring site).

Beyond Web Server logging, your IP address can also be captured within firewall log files. While Web server log files will provide information about legitimate access to Web pages, a firewall will also capture any attempted access that may be illegitimate, such as port scan attempts from your machine. While we all want strong logging to help stop bad guys and act as a deterrent, many types of attacks can be proxied through a third-party machine, such as your own. Being caught in the middle of an investigation into a hack attempt can happen to you.

ISPs will also regularly log the IP address assigned to you, and when you log on, as part of RADIUS authentication systems. These systems have often been used for billing systems, but the information is often retained even when you have a flat fee service agreement.

Getting more information from captured IP addresses. Once someone has your IP address, it can yield additional information about you from a query to one of the network address registries. By using the whois command, one can tell which company or organization owns your address:

whois would be replaced by the specific IP address you are checking. can be replaced by for European addresses and for Asia/Pacific addresses. These queries typically include information such as your company's mailing address and the network administrator's contact information.

It is also possible to uncover information about your IP address from DNS. By using the traceroute command, one can trace the routing path taken from their node to yours, and might be able to learn the geographic location you dialed in from. For ease of management, ISPs like to use DNS to assign a geographic location to the IP addresses of their equipment, often down to the city. So even if you get a different IP address each time, your address may be traced to your ISP and the location you dialed into. While that may not necessarily mean you are in the same city, you are not often likely to purposely dial long distance when a local call will suffice.

When you surf the Internet, think of your PC as a slug leaving a slime trail wherever it goes. Combining the information above with any optional registration data you fill out at a Web site could leave your personal information fairly well exposed. Next week, in part two of this series, we'll take a look at some of the emerging options to hide your personal information.


Jim Reavis, the founder of, is an analyst with over 10 years' experience consulting with Fortune 500 organizations on networking and security-related technology projects. is a Web site dedicated to providing IT professionals with comprehensive information about network security issues. Jim can be reached at

It's easier than ever to spy on workers
Network World, 09/24/99

New Web tool tracks online shoppers
Network World, 09/20/99

U.S. lawmakers hear range of 'Net privacy opinion
Network World, 07/13/99

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