HAMBURG There are no secrets on the Internet. True, you can sit in the privacy of your home and click your way through the digital world away from the prying eyes of colleagues and neighbors.

Yet nothing can protect a surfer from another kind of intrusion of privacy on-line. Your "digital footprints" can be tracked by digital pursuers while you surf the net -- and you may never know you're being followed.

According to DPA, by examining the Internet Protocol Number (IP number) that uniquely identifies every computer that is connected to the Internet, those interested in tracking Internet users can determine when someone visited a particular site.

A self-test of how such tracking works can be found at www.netreal.de/test/ip, showing which information is saved during the download of an Internet site: The time, IP address, browser type, operating system, previously visited Internet sites, and the host servers through which the computer in question is accessing the Internet.

Further information on your movements on-line can be transmitted via "Cookies".

These are short strings of numbers that are saved on your computer when you call up a site. Cookies transmit information about what you do at a website, and how often you visit, for example.

More than anything else, this information benefits web advertisers.

More and more firms are employing professional data collection firms to build profiles of their Internet users so that they can advertise to them with more precision, according to reports by the Information Services Science (IDW) program run jointly by the German universities of Beyreuth, Bochum and Clausthal.

A person who goes on-line to reserve tickets to a computer fair, order a pizza, or purchase a book to be gift-wrapped can be pegged as a stressed-out computer worker, for example.

Hannes Federrath of the Institute for Computer Science at the Free University of Berlin believes that advertisers may go too far in mining data about your surfing habits.

He finds it plausible that life insurance companies would try to assemble inferences about you based upon surfing patterns before signing a contract.

"Imagine that you, the customer, have done a bit of web research into a serious disease from which a friend suffers.

"If they were to see this site in your history, the insurance company might offer you an unfavorable price," says Federrath.

The drive to collect data knows practically no limits. Many software firms use on-line updates of their software as a chance to peek into the configuration of the surfer's computer or to see which music is stored on their hard drives.

In some cases, this type of digital eavesdropping has piqued the interest of national authorities.

Moreover, European authorities such as Germany's Federal Bureau for Security in Information Technology (BSI) have seen signs that firms which collect data on-line through voluntary on-line forms don't just use that information for their own purposes but sell the information to third parties.

E-mail has also proven to be far less secure than a sealed envelope with a stamp.

"E-mail messages pass through a number of intersections before reaching their destination. Every person who has access to the server at that point can read the E-mail, change it, copy it, even delete it," claims a hacker with the moniker newb

rret.

There are also tools in circulation that allow one to "copy (mail) as it flies by," according to the hacker. Additionally, the E-mail provider also has access to the all correspondence.

Many experts presume that there is a systematic monitoring of worldwide E-mail traffic.

User groups hint again and again at an eavesdropping system of the American security services.

Newb

rret for one is convinced of its existence: "Naturally something like that could work, without leaving a trace behind."

The German BSI has done no more than collect information from the press about this theme. Still, BSI spokesman Michael Dickopf sees such an E-mail monitoring system as at least possible.

Users of peer-to-peer connections, as used on on-line music trading bazaars, are also leaving themselves open to undesired access of their private and sensitive data.

As part of an investigation, the on-line magazine ***Computer Channel*** turned up the bank, credit card, and insurance data of an eight- person American family using a peer-to-peer service such as Napster.

What's surprising is that such data spying is not necessarily criminal.

Anyone wanting to take part in the data exchange bazaars like Napster has to share part of his hard drive so that other users can download music texts, song lyrics or videos.

Help is possible with encryption technology for E-mail messages and anonymity services for the Internet. With the program Pretty Good Privacy (PGP) (www.pgp.com), E-mail messages can by encrypted and marked with a digital signature.

Newb

rret suggests going so far as turning off browser support of Cookies, Java Code, and Activex.

A research team from the Free University of Berlin has developed the anonymity software "Java Anon Proxy," which wipes away a surfer's data trail. A similar service is offered through the Internet site http://www.anonymizer.com.

There can be no such thing as absolute anonymity, says BSI's Dickopf: "Some data has to be given up in order to make the communication possible." The Internet provider needs data for billing purposes, for example.

Still, personal data should only be given to trustworthy providers. "A healthy mistrust is a good thing here," advises Dickopf.