Every high school kid who has built a Web page knows about “word stuffing,” the trick of embedding invisible words in the HTML coding so that search engines will serve up your site when someone searches those words. Generally, the idea is to embed words that are searched often: “Sex” is a reliable choice.

But as the practice spread to the business world, it took some new twists. National Envirotech Group, a pipeline reconstruction company, for example, chose the nifty marketing strategy of “stuffing” the name of a larger competitor, Insituform Technologies Inc., into its Web page. When someone searched for Insituform, they might be sent Insituform’s URL, but the URL of National Envirotech would be sent along as well. Insituform’s lawyers were not amused. In a lawsuit filed in New Orleans, they argued that anyone searching for their company might think Envirotech was affiliated with it.

Envirotech claimed that it had done nothing wrong because there is no law that prohibits the use of trade names in the key word of Web sites. Despite its alleged innocence, Envirotech settled and removed the disputed material.

Other cases, such as one involving a Web site operator who embedded references to Playboy magazine in his pages, offer a more helpful model for clever Web developers. The judge in that case ordered the removal of the contested terms on the grounds that they infringed on Playboy’s trademark. Just because you can’t see it doesn’t mean it can’t put you in jail.