The Web can be a treacherous place. There are the quack health sites, the hate sites, and the porn sites, if you don't watch where you're going. There are those who want to hack into your computer and use it to launch attacks against others, if you don't protect yourself.

And there's the threat of legal problems in putting up your own Web site, if you're not careful.

I recently experienced the reality of our legal system after I put up a small educational site about coin collecting, a hobby of mine. I named the site "Electronic Coin Collector's Survival Guide," and soon afterward I received a three-page letter sent via Federal Express demanding that I change the site's name.

The letter came from a lawyer representing the author of the book The Coin Collector's Survival Manual. It seemed that my name was too close to his and a potential trademark infringement. I quickly changed the name of my site to "Electronic Coin Collector's Guide," writing back to the lawyer that a two-sentence e-mail message would have achieved the same result.

I'm far from alone in receiving cease-and-desist "nastygrams" such as this. Disney, for instance, is famous for aggressively protecting its trademarks and copyrights, both online and off.

In one widely publicized case, Disney ordered three daycare centers in Florida to remove images of Mickey Mouse and other Disney characters displayed on their walls or pay licensing fees for them. (A trademark is typically a word or design that helps a company sell the product it's associated with, while a copyright is the legal right to control how writing, artwork, songs, movies, and so on can be used.)

In fairness, the courts have ruled over the years that businesses have to vigorously defend their trademarks or risk losing them to the public domain, which would prevent them from profiting from the trademarks.

One way they do this is through the cease-and-desist letter or e-mail message, or nastygram. "A nastygram is typically just a signal that the trademark holder wants you to stop using his trademark," says Stuart Mayer, a partner at Mayer Fortkort & Williams, an intellectual property law firm with offices in New Jersey, Virginia, and Texas [http://www.mfwlaw.com].

With trademarks, the key test is whether there could be any confusion in the mind of a reasonable person that your name is endorsed or supported by the owner of a trademarked name, says Mayer. Also important, he says, is if you've caused the trademark owner lost profits or if you've earned profits yourself as a result.

It can be difficult deciding how close your name can be to a trademarked name before you run the risk of trademark infringement. The more recognizable the trademark, the more latitude the courts will give the trademark owner, says Mayer.

National brands receive the most protection. "With McDonald's, you can have a problem with almost anything you put 'Mc' in front of, it if it looks like you're trying to trade on the McDonald's name, trying to take advantage of it," says Mayer. McDonald's was able to stop a hotel, for instance, from using the name McBed's, which implies quick and inexpensive.

But some companies go overboard with trademark, copyright, defamation, and related intellectual property and free speech issues, flinging out nastygrams indiscriminately, which can have a chilling effect on communication. In response, last year the Electronic Frontier Foundation, working with legal clinics at Harvard University, Stanford University, the University of California at Berkeley, and the University of San Francisco, put up a Web site called Chilling Effects [http://www.chillingeffects.org].

"The site is intended to serve as a tool for Internet users to understand their legal rights in the face of potentially intimidating and confusing cease-and-desist letters," says spokesperson Donna Wentworth.

Along with providing information about online trademark and copyright issues, the site offers advice about a host of related legal topics that affect Internet users, including e-commerce patents, "John Doe" anonymity, defamation, piracy, fan fiction, and protest, parody and criticism sites.

The site also invites Internet users to submit any nastygrams they may have received. Students at the participating law school clinics review and annotate them with links to explain the applicable legal rules.

"The Internet makes it easier for individuals to speak to a wide audience, but it also makes it easier for other people and corporations to silence that speech," says Wendy Seltzer, who conceived the project. "Chilling Effects aims to level the field by helping online speakers to understand their rights in the face of legal threats.