Hide and seek on the Web

So he tried passive resistance by drawing a virtual curtain around his Web site. The trick, called cloaking, made his blog appear seemingly abandoned to her, while his regular postings were available to anyone else with a Web browser.

"I found out the Internet Protocol address (of her computer) and delivered her a static page anytime she visited," said Allen, an author and software developer. "That worked really well, until one day she went to an Internet cafe and found a month-and-a-half worth of postings and left a bunch of ugly comments again."

Allen added: "Still, it's a really neat idea to be able to cloak a page."

The concept, also known as IP-based filtering, has been around for many years, and outside of dodging an ex, it has numerous useful and covert applications that have caught on in the business world.

While few would admit it, the practice is an ever-more-popular strategy for Web site operators and corporations playing espionage with rivals.

Footprints left in the form of Web traffic logs are tipping one kind of voyeur off to another, and in some cases, that's delivered new competitive intelligence to rivals.

An online retailer, for example, might show one price for a digital camera to the public, and another price 15 percent higher for the same product to its rival. Consequently, the rival might price its product disproportionately and lose customers.

"Like with Caller ID, people want to know who's calling them. And it's going that way now with the computer; people want to know who's looking at their site," said Chris Cox, a Florida-based private investigator. "Some of (the voyeurism) is quite general, like for marketing purposes, and some of it can be quite sinister."

As the Internet becomes part of mainstream media, several high-profile lawsuits, including those from the music labels, have proven that privacy is anything but a guarantee online. But people still have the feeling they're anonymous while surfing. That's why many "safe surfing" or subscription privacy tools have yet to gain steam with consumers.

Fears that marketers are watching your every move have subsided and seemingly been replaced by corporate paranoia over internal secrets.

New tools to help companies "cloak" their traffic while surfing the Web are becoming an attractive defense as a result.

Privately held Anonymizer, based in San Diego, began selling a corporate Internet cloaking service in 2003 called the Enterprise Chameleon. The product, a piece of hardware and software linked to a corporate server, will filter all employee traffic through its IP-changing servers and randomly issue untraceable IP addresses.

Sales of the product jumped 500 percent from 2003 to 2004, and this year the company expects corporate sales to comprise 50 percent of its revenue. (The other half comes from individual customers.) Anonymizer caters to government agencies and corporations, including pharmaceutical and biotechnology companies.

In general, cloaking works through a simple script that commands the Web server to deliver a set Web page whenever it detects the designated IP address. The IP address can be traced to an Internet service provider and, with special tools, to a geographic location. Because IP addresses are often static, the script could also mark whole blocks of numbers assigned to an Internet service provider, a geographic range, a specific company or government entity.

In one practical example of IP-based filtering called geo-targeting, an online retailer can display Polar Fleece clothing to Alaskans by detecting their IP address and hence, their whereabouts. Advertisers use the same technology to send specific promotions to consumers, and search engines sniff IP addresses to display results based on a user's locale.